Abstract:
A method is described that is particularly effective for the filtration of an aquarium by means of a filtration unit wherein a cartridge containing activated carbon is cyclically replaced by a cartridge containing material for the removal of nitrate and/or phosphate ions. A plurality of mechanical filters may also be alternately replaced, so that a colony of nitrifying bacteria is always preserved on one of the filters. Also described is a filtration unit that allows the application of the method and a replacement kit containing both the cartridge containing activated carbon and the cartridge containing material for the removal of nitrate and/or phosphate ions, and preferably also one of the mechanical filters.

Description:
FIELD OF APPLICATION 
       [0001]    The present invention, in its most general aspect, refers to a method for filtering aquarium water, in particular for a domestic aquarium. 
         [0002]    The invention also refers to a filtration unit, possibly integrated in an aquarium, as well as a replacement kit, both intended to allow the above-mentioned filtration method to be applied. 
       PRIOR ART 
       [0003]    As is well known to those skilled in the art, the correct maintenance of an aquarium generally requires constant circulation and filtration of the water that contains the fish species kept in the aquarium. 
         [0004]    To ensure that these requirements are met, specific filtration units are used, inside of which the water is made to circulate along a predetermined filtration path. Such filtration units draw in water from the aquarium tank and reintroduce it purified, after passing through said filtration process. 
         [0005]    The filtration of the water takes place in several steps, each connected with separate subsequent stages in the filtration unit. More particularly up to three different stages may be present, respectively called mechanical, biological and chemical filtration. 
         [0006]    The stage of mechanical filtration, intended to remove the coarser particulate matter present in the water, makes use of a special sponge, usually made of polyurethane material. The water flows straight through the sponge while the material suspended in the water is retained by it. 
         [0007]    One will note that these sponges are subject to clogging and therefore must be periodically replaced to ensure continued effectiveness of the filter installation. 
         [0008]    Preferably downstream from the mechanical filtration the stage of biological filtration takes place, defined by a compartment filled with solid elements, generally made of a ceramic material characterized by a high surface/volume ratio. The surfaces of these elements promote the formation of colonies of nitrifying bacterial flora that break down the toxic nitrogenous catabolites in the water (such as ammonium and nitrite) into compounds that are less harmful to the fish population of the aquarium (nitrates). 
         [0009]    Lastly the chemical filtration stage includes the use of filtration material intended to remove other unwanted compounds such as nitrates, phosphates and organic compounds. In particular ion-exchange resins are used to remove nitrate and phosphate ions, whereas for the removal of organic compounds preferably activated carbon is used. 
         [0010]    One should note that the effectiveness of the materials used in the chemical filtration stage diminishes rapidly over time due to saturation, which necessitates periodical replacement. 
         [0011]    The removal of nitrates and phosphates from the aquarium water is mainly intended to prevent the proliferation of algae inside the aquarium tank; the removal of organic substances, on the other hand, is above all aimed at avoiding deterioration of water quality. 
         [0012]    Ideally it would be preferable to have a filtration stage with both the anti-phosphate and anti-nitrate resins and the activated carbon. However such a solution would result in a greater size and shape of the chemical filter, which would in many cases be incompatible with the available space in the filtration unit. In view of this drawback, suppliers often opt to eliminate one of the filtration stages described above. 
         [0013]    Again from the point of view of reducing the dimensions of the filtration unit, in some cases a separate stage of biological filtration is eliminated, confiding instead in the proliferation of nitrifying bacteria on the polyurethane sponge that forms the mechanical filtration stage. 
         [0014]    This solution, although on the one hand allowing for reduced sizes, on the other hand creates a drawback in connection with the periodical replacement of the mechanical filter. Each time the filter is replaced, the bacterial flora are removed and a certain period of time is necessary for them to reform and again ensure adequate biological filtration. 
       SUMMARY OF THE INVENTION 
       [0015]    The technical problem at the basis of the present invention is that of finding a filtration method that guarantees complete efficacy in the different filtration stages, allowing at the same time that the filter unit remains compact and low-cost. 
         [0016]    The above-mentioned technical problem is resolved by a method for filtering the water in an aquarium by means of a filtration unit, said method comprising: 
         [0017]    leading water circulation along a filtration path that comprises at least a chemical filtration stage, said chemical filtration stage comprising at least a cartridge containing activated carbon or a cartridge containing material for the removal of nitrate and/or phosphate ions; 
         [0018]    cyclically replacing said cartridge, over time alternating between cartridges with activated carbon and cartridges with material for the removal of nitrate and/or phosphate ions. 
         [0019]    Thanks to the constant alternation between cartridges with activated carbon and cartridges with material for the removal of nitrate and/or phosphate ions, an optimal filtration balance is obtained, preventing the formation of algae as well as deterioration of water quality. This result is obtained by using cartridges that are small in size, without negatively impacting maintenance costs of the installation. 
         [0020]    In a particular embodiment of the above-mentioned method the filtration path also comprises at least a mechanical filtration stage, said mechanical filtration stage comprising at least two mechanical filters. The method thus comprises the following cyclically repeating steps: 
         [0021]    replacing a number of mechanical filters less than the total number of mechanical filters in the mechanical filtration stage; 
         [0022]    replacing, in a subsequent moment, a number of mechanical filters less than the total number of mechanical filters in the mechanical filtration stage, said number of filters at least containing the mechanical filters that have not been replaced in the previous step. 
         [0023]    This way of replacing the mechanical filters makes it possible to retain at the end of each maintenance operation at least one mechanical filter (preferably consisting of a polyurethane sponge) that has already been used in the previous filtration cycle. This solution proves to be particularly advantageous because the already used filter will contain a colony of nitrifying bacteria that performs an important biological filtration of the water circulating in the filtration unit. 
         [0024]    Other particularly advantageous embodiments of the method according to the invention are described in the dependent claims of the present application. 
         [0025]    The method described above can be implemented by a filtration unit for aquaria that comprises a filtration path and means to lead the circulation of aquarium water along said path, said filtration path comprising at least one chemical filtration stage containing alternately and in a replaceable manner a cartridge containing activated carbon or a cartridge containing material for the removal of nitrate and/or phosphate ions. 
         [0026]    Other particularly advantageous embodiments of the filtration unit are described in the dependent claims of the present application. 
         [0027]    The method described above can be implemented by using a replacement kit for filter units for aquaria comprising a cartridge containing activated carbon and a cartridge containing material for the removal of nitrate and/or phosphate ions, said cartridges being able to replace each other inside the aquarium filter unit. 
         [0028]    The kit preferably also comprises a mechanical filter, in particular a polyurethane sponge or other type. 
         [0029]    Further characteristics and advantages of the invention will become clear from the following description of a number of specific embodiments given by way of non-limiting example, with reference to the enclosed drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  schematically represents a small-sized aquarium comprising a filtration unit according to the present invention; the continuous arrows indicate a filtration path inside the unit; 
           [0031]      FIG. 2  represents a flowchart for the filtration method according to the present invention, obtained with the filtration unit of  FIG. 1 ; 
           [0032]      FIG. 3  schematically represents a medium-sized aquarium comprising a filtration unit according to the present invention; the continuous arrows indicate a filtration path inside the unit; 
           [0033]      FIG. 4  represents a flowchart for the filtration method according to the present invention, obtained with the filtration unit of  FIG. 3 ; 
           [0034]      FIG. 5  schematically represents a large-sized aquarium comprising a filtration unit according to the present invention; the continuous arrows indicate a filtration path inside the unit; 
           [0035]      FIG. 6  represents a flowchart for the filtration method according to the present invention, obtained with the filtration unit of  FIG. 5 ; 
           [0036]      FIG. 7  schematically represents a very large-sized aquarium comprising a filtration unit according to the present invention; the continuous arrows indicate a filtration path inside the unit; 
           [0037]      FIG. 8  represents a flowchart for the filtration method according to the present invention, obtained with the filtration unit of  FIG. 7 ; 
           [0038]      FIG. 9  schematically represents a replacement kit to be used for the filtering method of  FIG. 2 ; 
           [0039]      FIG. 10  schematically represents a replacement kit to be used for the filtration methods of  FIGS. 4 ,  6 ,  8 ; 
           [0040]      FIG. 11  represents an electronic device for the realization of the filtration methods of  FIGS. 2 ,  4 ,  6 ,  8 ; 
           [0041]      FIG. 12  represents a flowchart of the functionality of the electronic device of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    The present invention regards a method for filtering the water in an aquarium, as well as a filtration unit incorporated in an aquarium and a replacement kit specifically designed for said filtration method. 
         [0043]    The following describes in detail four different embodiments of the filtration unit, intended for aquaria progressively increasing in size. To differentiate between them in the following description, the four variants are identified as  1   S ,  1   M ,  1   L  and  1   XL , with the subscript indicating the progressively increasing size of the device. 
         [0044]    For each variant of the filtration unit a respective embodiment of the filtration method is described. The different embodiments of the filtration unit and the filtration method are illustrated in the attached drawings  1 - 8 . Where possible the same reference numbers have been used to indicate the same components or steps of the procedure, sometimes followed by the subscript S, M, L or XL to indicate the filtration unit being referred to. 
         [0045]    Note that the filtration units are represented in the respective figures in accordance with their normal operational configuration; in the following description, all positions and orientations, both relative and absolute, of the various components of the unit, defined by means of terms such as upper and lower, above and below, horizontal and vertical or similar terms, should always be interpreted with reference to that configuration. 
         [0046]    For all variants of the filtration unit described below the replacement kit  200   S ,  200  is required. A first replacement kit  200   S , for use with the filtration unit  1   S , is represented in  FIG. 9 ; a second replacement kit  200 , intended for use with the filtration units  1   M ,  1   L ,  1   XL , is represented in  FIG. 10 . 
         [0047]    Both replacement kits  200   S ,  200  contain three separate components: a mechanical filter  2   S ,  2 ; a cartridge containing activated carbon  4   a   S ,  4   a ; and a cartridge containing material for the removal of nitrate and/or phosphate ions  4   b   S ,  4   b . In the preferred embodiment described here the mechanical filter  2   S ,  2  is formed by a sponge made of a polyurethane material. The cartridges  4   a   S ,  4   a ,  4   b   S , consist of an external container, through which opportunely the water to be filtered can pass, containing the active material. To allow the passage of the water that is to be filtered at least two faces of the cartridge are pervious; preferably all lateral surfaces, the top surface and the bottom surface of the cartridge are pervious. The material for the removal of nitrate ions and/or phosphate can be in the form of resins known from prior art. In the following description the cartridges containing the activated carbon  4   a   S ,  4   a  and the cartridges containing the material for the removal of nitrate and/or phosphate ions  4   b   S ,  4   b  will both be called chemical filtration cartridges. 
         [0048]    An ideal service period T of two weeks is indicated for the chemical filtration cartridges,  4   a   S ,  4   a ,  4   b   S ,  4   b , after which the cartridges will become saturated and lose much of their filtration capacity. For the mechanical filters  2  an ideal service period 2·T of four weeks is indicated. After that time limit the filters will become clogged and lose much of their filtration capacity. 
         [0049]    The components contained in the first replacement kit  200   S  and the second replacement kit  200  differ in their relative sizes; in particular the components of the first replacement kit  200   S  are smaller in size. 
         [0050]    With reference to  FIG. 1  the number  100   S  identifies a small-sized aquarium into which the filtration unit  1   S  is integrated at the top. 
         [0051]    The filtration unit  1   S  comprises a pump  5   S  that draws in the water inside the aquarium  100   S  to circulate it along a filtration path  7   S ;  20   S ;  8   S ;  40   S . 
         [0052]    The pump  5   S , located upstream of the filtration path  7   S ;  20   S ;  8   S ;  40   S , leads the water through a delivery duct  7   S . The duct ends in a vertical passage that connects with the upper end of the filtration unit  1   S , which opens into a first compartment  20   S . 
         [0053]    The first compartment  20   S  is designed to house two mechanical filters  2   S , of the type contained in the first replacement kit  200   S  previously described. The two mechanical filters  2   S  are placed one above the other and they rest on an open grid that covers a connecting duct  8   S . The water coming from the delivery duct  7   S  then passes through the two mechanical filters  2   S  by gravitational effect, where the particulate matter suspended in the water is captured, thus performing the mechanical filtration. Note that on the sponges that form the mechanical filters  2   S  in time nitrifying bacterial flora will establish themselves. After the formation of these flora, the mechanical filters will in this way also perform a biological filtration of the water that passes through them. 
         [0054]    In the light of the above the first compartment  20   S  thus defines a mechanical/biological filtration stage of the filtration unit  1   S . 
         [0055]    The connection duct  8   S  extends below a second compartment  40   S , contiguous with the first compartment and separated from it by means of a vertical partition  9   S  above the duct. This second compartment has an open grid at the bottom that separates it from the connection duct  8   S  and it can receive a cartridge containing activated carbon  4   a   S , or alternately a cartridge containing material for the removal of nitrate and/or phosphate ions  4   b   S . Both cartridges are of the type contained in the first replacement kit  200   S  previously described. The water coming from the connection duct  8   S  thus enters the second compartment  40   S  at the lower end and is subsequently reintroduced into the aquarium  100   S  through an open exit grid  6   S  opposite the vertical partition  9   S . The water that passes through the second compartment  40   S  transits through the interior of the cartridge  4   a   S ,  4   b   S  inserted in the compartment, by means of its pervious surfaces. In this way the cartridge  4   a   S ,  4   b   S  performs a chemical filtration of the circulating water. 
         [0056]    In the light of the above the second compartment  40   S  thus defines a chemical filtration stage of the filtration unit  1   S . 
         [0057]      FIG. 2  presents a flowchart of a filtration method that uses the filtration unit  1   S  described previously. 
         [0058]    In a preliminary phase  1000   S  a starting configuration of the filtration unit  1   S  is established. In this starting configuration there are two mechanical filters  2   S  located one on top of the other inside the first compartment  20   S  and a cartridge containing activated carbon  4   a   S  inside the second compartment  40   S . 
         [0059]    During a subsequent preliminary waiting period  1100   S  the filtration unit  1   S  is operational for a time period equal to the service period 2·T of the mechanical filters  2   S , i.e. for four weeks. 
         [0060]    During operation the water, by means of the pump  5   S , is led along the filtration path  7   S ;  20   S ;  8   S ;  40   S  inside the filtration unit  1   S . 
         [0061]    With the passage of time the mechanical filters  2   S  will become progressively clogged up; contemporaneously, however, they become the seat of nitrifying bacterial flora that contribute to the biological filtration of the water. 
         [0062]    In the meantime the activated carbon in the cartridge  4   a   S  proceeds with the removal of organic material to maintain high water quality in the aquarium  100   S . In the meantime, however, the phosphates and nitrates that have not been removed will accumulate in the water, so that after four weeks an environment has developed that stimulates algal proliferation; also the cartridge containing activated carbon  4   a   S  will increasingly become saturated and less efficacious. 
         [0063]    In a subsequent first replacement step  1200   S  the filters are replaced after four weeks have elapsed. 
         [0064]    For the replacement the elements contained in a replacement kit  200   S  are used. 
         [0065]    The by now saturated cartridge containing activated carbon  4   a   S  is replaced by the cartridge containing material for the removal of nitrate and/or phosphate ions  4   b   S  of the replacement kit  200   S . The new cartridge will break down the nitrates/phosphates in the water, thus preventing the development of an environment that would be favorable to the formation of algae. 
         [0066]    The topmost mechanical filter  2   S , most likely also clogged up, is removed. In its stead the mechanical filter  2   S  previously located below is inserted. This filter is not yet clogged up, given that it was downstream from the first filter; in exchange nitrifying bacterial flora have developed on it, which are necessary for efficacious biological filtering. In the opened up lower position a new mechanical filter  2   S  from the replacement kit  200   S  is inserted. 
         [0067]    Note that the replacement of the mechanical filters  2   S  in the manner described above presents the advantage of having at all times a mechanical filter  2   S  with nitrifying flora that perform the biological filtration. Thanks to this operation the filtration unit  1   S  can contain one less separate biological filtration stage. 
         [0068]    The new cartridge containing activated carbon  4   a   S , present in the replacement kit  200   S , is not used at this moment but set aside for future use. 
         [0069]    During a subsequent first waiting period  1300   S  the filtration unit  1   S  is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a   S ,  4   b   S , i.e. for two weeks. 
         [0070]    During this stage phosphates and nitrates are removed, preventing the formation of algae; in the meantime organic detritus accumulates that could lead in the subsequent period to a deterioration in water quality. 
         [0071]    Efficacious biological filtration is performed by the bacterial flora present on the old mechanical filter  2   S  placed in the top position; in the meantime new bacterial flora are formed on the new mechanical filter  2   S  in the lower position. 
         [0072]    In a subsequent second replacement step  1400   S  only the chemical filter is replaced after two weeks have elapsed. 
         [0073]    The now saturated cartridge containing material for the removal of nitrate and/or phosphate ions  4   b   S  is replaced by the cartridge containing activated carbon  4   a   S  previously set aside. The new cartridge will absorb the organic detritus, thereby preventing a deterioration in water quality. 
         [0074]    During a subsequent second waiting period  1500   S  the filtration unit  1   S  is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a   S ,  4   b   S , i.e. for two weeks. 
         [0075]    During this stage the activated carbon contained in the cartridge  4   a   S  removes the organic pollution, while in the meantime phosphates and nitrates re-accumulate. The topmost mechanical filter  2   S  begins to clog up; whereas on the lower mechanical filter nitrifying bacterial flora have established themselves. 
         [0076]    At the end of this second waiting period  1500   S , the following steps are cyclically repeated: the first replacement step  1200   S ; the first waiting phase  1300   S ; the second replacement step  1400   S ; and the second waiting phase  1500   S . 
         [0077]    With reference to  FIG. 3  the number  100   M  identifies a medium-sized aquarium into which the filtration unit  1   M  is integrated at the top. The filtration unit  1   M  comprises a pump  5   M  that draws in the water inside the aquarium  100   M  to circulate it along a filtration path  7   M ;  20   M ;  30   M ;  40   M . 
         [0078]    The pump  5   M , located at the bottom of the aquarium  100   M  and upstream of the filtration path  7   M ;  20   M ;  30   M ;  40   M , leads the water through a delivery duct  7   M . The duct reaches an upper end of the filtration unit  1   M , at the point where it opens into a first compartment  20   M . 
         [0079]    The first compartment  20   M  is delimited by a vertical partition  9   M  and a horizontal partition  10   M . The vertical partition  9   M , opposite the wall onto which the delivery duct  7   M  opens, divides the first compartment  20   M  from an adjacent third compartment  40   M . Through the vertical partition  9   M  an upper overflow hole passes that allows the water to flow out of the first compartment  20   M  in case of overfilling. The horizontal partition  10   M  closes the first compartment  20   M , separating it from a second compartment  30   M  below, in communication with the third compartment  40   M . The horizontal partition is traversed by an outflow hole located near the wall onto which the delivery duct  7   M  opens. 
         [0080]    The first compartment  20   M  is designed to house a mechanical filter  2 , of the type contained in the second replacement kit  200  previously described. The mechanical filter  2  covers the horizontal partition  10   M , so that the water coming from the delivery duct  7   M  passes through it by gravitational effect, to reach the outflow hole made in that partition. The mechanical filter  2  captures the particulate matter suspended in the water passing through it, thus performing the mechanical filtration. 
         [0081]    In the light of the above the first compartment  20   M  thus defines a mechanical filtration stage of the filtration unit  1   M . 
         [0082]    The second compartment  30   M  is designed to house a cartridge for biological filtration  3 . This cartridge  3  consists of an external container, through which opportunely the water to be filtered can pass, containing elements that promote the formation of nitrifying bacterial flora on their surfaces. These elements are preferably in the form of porous ceramic cylinders. To allow the passage of the water that is to be filtered, at least the lateral surfaces of the biological filtration cartridge are pervious. 
         [0083]    Note that the biological filtration cartridge  3  is preferably inserted in an extractable manner inside the filtration unit  1   M . To allow the cartridge to be extracted the horizontal partition  10   M  can be removed, or can even be formed by an upper non-pervious surface of the biological filtration cartridge  3 . 
         [0084]    The water that enters the second compartment  30   M  through the outflow hole of the horizontal partition  10   M  passes through the entire biological filtration cartridge  3  before reaching the adjacent third compartment  40   M . In this way the cartridge  3  filters the water biologically, breaking down toxic nitrogenous compounds into nitrates. 
         [0085]    In the light of the above the second compartment  30   M  thus defines a biological filtration stage of the filtration unit  1   M . 
         [0086]    The third compartment  40   M  is designed to house a cartridge containing activated carbon  4   a , or alternately a cartridge containing material for the removal of nitrate and/or phosphate ions  4   b . Both cartridges are contained in the first replacement kit described previously. The water coming from the second compartment  30   M  passes through the third compartment  40   M  before being returned to the aquarium  100   M  through an opposite exit opening  6   M . The water that passes through the third compartment  40   M  therefore transits through the interior of the cartridge  4   a ,  4   b  inserted in the compartment, by means of its pervious surfaces. In this way the cartridge  4   a ,  4   b  performs a chemical filtration of the circulating water. 
         [0087]    In the light of the above the third compartment  40   M  thus defines a chemical filtration stage of the filtration unit  1   M . 
         [0088]      FIG. 4  presents a flowchart of a filtration method that uses the filtration unit  1   M  described previously. 
         [0089]    In a preliminary phase  1000   M  a starting configuration of the filtration unit  1   M  is established. In this starting configuration there is a mechanical filter  2  located inside the first compartment  20   M , a cartridge for biological filtration  3  inside the second compartment  30   M , and a cartridge containing activated carbon  4   a  inside the third compartment  40   M . 
         [0090]    During a subsequent preliminary waiting period  1100   M  the filtration unit  1   M  is operational for a time period equal to the service period 2·T of the mechanical filters  2 , i.e. for four weeks. 
         [0091]    During operation the water, by means of the pump  5   M , is led along the filtration path  7   M ;  20   M ;  30   M ;  40   M  inside the filtration unit  1   M . 
         [0092]    With the passage of time the activated carbon of the cartridge  4   a  will remove organic pollution, keeping the water of the aquarium  100   M  clean. In the meantime, however, the phosphates and nitrates that have not been removed will accumulate in the water, so that after four weeks an environment has developed that stimulates algal proliferation; also the cartridge containing activated carbon  4   a  will increasingly become saturated and less efficacious. 
         [0093]    The material contained by the biological filtration cartridge  3  in the meantime has become the seat of nitrifying flora that effectively eliminate the toxic nitrogenous compounds in the water. 
         [0094]    In a subsequent first replacement step  1200   M  the filters are replaced after four weeks have elapsed. 
         [0095]    For the replacement the elements contained in a replacement kit  200  are used. 
         [0096]    The by now saturated cartridge containing activated carbon  4   a  is replaced by the cartridge containing material for the removal of nitrate and/or phosphate ions  4   b   S  of the replacement kit  200 . The new cartridge will break down the nitrates/phosphates in the water, thus preventing the development of an environment that would be favorable to the formation of algae. 
         [0097]    The mechanical filter  2 , most likely clogged up, is replaced by the new mechanical filter from the replacement kit  200 . 
         [0098]    The new cartridge containing activated carbon  4   a  of the replacement kit  200  is not used at this moment but set aside for future use. 
         [0099]    During a subsequent first waiting period  1300   M  the filtration unit  1   M  is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a ,  4   b , i.e. for two weeks. 
         [0100]    During this stage phosphates and nitrates are removed, preventing the formation of algae; in the meantime organic detritus accumulates that could lead in the subsequent period to a deterioration in water quality. 
         [0101]    In a subsequent second replacement step  1400   M  only the chemical filter is replaced after two weeks have elapsed. 
         [0102]    The by now saturated cartridge containing material for the removal of nitrate and/or phosphate ions  4   b  is replaced by the cartridge containing activated carbon previously set aside. The new cartridge will absorb the organic detritus, thereby preventing deterioration in water quality. 
         [0103]    During a subsequent second waiting period  1500   M  the filtration unit  1   M  is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a ,  4   b , i.e. for two weeks. 
         [0104]    During this stage the activated carbon contained in the cartridge  4   a  removes the organic pollution, while in the meantime phosphates and nitrates re-accumulate. 
         [0105]    At the end of this second waiting period  1500   M , the following steps are cyclically repeated: the first replacement step  1200   M ; the first waiting phase  1300   M ; the second replacement step  1400   M ; and the second waiting phase  1500   M . 
         [0106]    With reference to  FIG. 5  the number  100   L  identifies a large-sized aquarium into which the filtration unit  1   L  is integrated at the top. The filtration unit  1   L  is structurally identical to the previously described unit for medium-sized aquaria  1   M , with the exception of different dimensions of the compartments to allow a greater number of filtration elements to be introduced. 
         [0107]    In particular the filtration unit  1   L  comprises a pump  5   L  with delivery duct  7   L ; a first  20   L , second  30   L  and third  40   L  compartment, divided from each other by a vertical partition  9   L  and a horizontal partition  10   L ; and an open exit grid  6   L , whose configurations are all analogous to the corresponding elements described with reference to the filtration unit  1   M  for medium-sized aquaria. 
         [0108]    The only substantial difference is the horizontal dimension of the first  20   L  and the second  30   L  compartments, which are respectively designed to house two mechanical filters  2  and two biological filtration cartridges  3 . 
         [0109]    The biological filtration cartridges  3  are located in series along the filtered water&#39;s direction of circulation; in other words a first cartridge abuts against the wall contiguous to the delivery duct  7   L , whereas the second cartridge is located in proximity to the third compartment  40   L . In this way the water coming from the first compartment  20   L  passes through both biological filtration cartridges  3  before arriving at the third compartment  40   L . 
         [0110]    The mechanical filters  2  are substantially placed over the two biological filtration cartridges  3 . In this way the water coming from the delivery duct  7   L  can reach the bottom of the first compartment  20   L  passing through either of the two mechanical filters  2 . For the present purposes the mechanical filter  2  closest to the outlet of the delivery duct  7   L  will be called the upstream filter, while the filter  2  nearer the vertical partition  9   L  will be called the downstream filter. 
         [0111]      FIG. 6  presents a flowchart of a filtration method that uses the filtration unit  1   L  described previously. 
         [0112]    The method described in detail below, is substantially analogous to the one described previously in relation to the filtration unit  1   M ; all previous considerations presented with reference to the operation of the filters as a result also apply to the present method. 
         [0113]    In a preliminary phase  1000   L  a starting configuration of the filtration unit  1   L  is established. In this starting configuration there are two mechanical filters  2  juxtaposed inside the first compartment  20   L , two cartridges for biological filtration  3  inside the second compartment  30   L  and a cartridge containing activated carbon  4   a  inside the second compartment  40   L . 
         [0114]    During a subsequent preliminary waiting period  1100   L  the filtration unit  1   L  is operational for a time period equal to the service period 2·T of the mechanical filters  2 , i.e. for four weeks. 
         [0115]    In a subsequent first replacement step  1200   L  the filters are replaced after four weeks have elapsed. 
         [0116]    For the replacement the elements contained in a replacement kit  200  are used. 
         [0117]    The cartridge containing activated carbon  4   a  is replaced by the cartridge containing material for the removal of nitrate and/or phosphate ions  4   b  of the replacement kit  200 . 
         [0118]    The upstream mechanical filter  2 , the one nearest the outlet of the delivery duct  7   L  and containing the greatest quantity of detritus, is removed. In its place the mechanical filter  2  previously located downstream is inserted. This filter is most likely less clogged; also nitrifying bacterial flora have developed on it, useful for the removal of toxic nitrogenous compounds. In the opened up downstream position a new mechanical filter  2  from the replacement kit  200  is inserted. 
         [0119]    The new cartridge containing activated carbon  4   a , present in the replacement kit  200 , is not used at this moment but set aside for future use. 
         [0120]    During a subsequent first waiting period  1300   L  the filtration unit  1   L  is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a ,  4   b , i.e. for two weeks. 
         [0121]    In a subsequent second replacement step  1400   L  the cartridge containing material for the removal of nitrate and/or phosphate ions  4   b  is replaced by the cartridge containing activated carbon  4   a  previously set aside. 
         [0122]    During a subsequent second waiting period  1500   L  the filtration unit  1   L  is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a ,  4   b , i.e. for two weeks. 
         [0123]    At the end of this second waiting period  1500   L , the following steps are cyclically repeated: the first replacement step  1200   L ; the first waiting phase  1300   L ; the second replacement step  1400   L ; and the second waiting phase  1500   L . 
         [0124]    With reference to  FIG. 7  the number  100 X L  identifies a very large-sized aquarium into which the filtration unit  1   XL  is integrated at the top. The filtration unit  1   XL  is structurally identical to the previously described unit for medium-sized aquaria  1   M , with the exception of different dimensions of the compartments to allow a greater number of filtration elements to be introduced. 
         [0125]    In particular the filtration unit  1   XL  comprises a pump  5   XL  with delivery duct  7   XL ; a first  20   XL , second  30   XL  and third  40   XL  compartment, divided from each other by a vertical partition  9   XL  and a horizontal partition  10   XL ; and an open exit grid  6   XL , whose configurations are all analogous to the corresponding elements described with reference to the filtration unit  1   M  for medium-sized aquaria. 
         [0126]    The only substantial difference is the horizontal dimension of the first  20   XL , second  30   XL  and third  40   XL  compartments, which are respectively designed to house three mechanical filters  2 , three biological filtration cartridges  3  and two chemical filtration cartridges  4   a  or  4   b.    
         [0127]    The biological filtration cartridges  3  are located in series along the filtered water&#39;s direction of circulation; in other words a first cartridge abuts against the wall contiguous to the delivery duct  7   XL , whereas the third and last cartridge is located in proximity to the third compartment  40   XL . In this way the water coming from the first compartment  20   XL  passes through the series of three biological filtration cartridges  3  before arriving at the third compartment  40   XL . 
         [0128]    The mechanical filters  2  are substantially placed above the three biological filtration cartridges  3 . In this way the water coming from the delivery duct  7   XL  can reach the bottom of the first compartment  20   XL  passing through any of the three mechanical filters  2 . For the present purposes the mechanical filter  2  closest to the outlet of the delivery duct  7   XL , will be called the upstream filter, while the filter  2  nearer the vertical partition  9   XL  will be called the downstream filter. 
         [0129]    The two cartridges containing activated carbon  4   a , or alternately containing material for the removal of nitrate and/or phosphate ions  4   b , are located in series along the filtered water&#39;s direction of circulation; in other words the first cartridge is located in proximity to the second compartment  30   XL  whereas the second cartridge rests on the open exit grid  6   XL . In this way the water coming from the first compartment  20   XL  or the second compartment  30   XL , passes through both cartridges before reentering the aquarium  100   XL . 
         [0130]      FIG. 8  presents a flowchart of a filtration method that uses the filtration unit  1   XL  described previously. 
         [0131]    The method described in detail below, is substantially analogous to the one described previously in relation to the filtration unit  1   M ; all previous considerations presented with reference to the operation of the filters as a result also apply to the present method. 
         [0132]    In a preliminary phase  1000   XL  a starting configuration of the filtration unit  1   XL  is established. In this starting configuration there are three mechanical filters  2  juxtaposed inside the first compartment  20   XL , three cartridges for biological filtration  3  inside the second compartment  30   XL  and two cartridges containing activated carbon  4   a  inside the third compartment  40   XL . 
         [0133]    During a subsequent preliminary waiting period  1100   XL  the filtration unit  1   XL  is operational for a time period equal to the service period 2·T of the mechanical filters  2 , i.e. for four weeks. 
         [0134]    In a subsequent first replacement step  1200   XL  the filters are replaced after four weeks have elapsed. 
         [0135]    For the replacement the elements contained in two replacement kits  200  are used. 
         [0136]    Both cartridges containing activated carbon  4   a  are replaced by two cartridges containing material for the removal of nitrate and/or phosphate ions  4   b  of the two replacement kits  200 . 
         [0137]    The upstream mechanical filter  2  and the middle filter, being the ones nearest the outlet of the delivery duct  7   XL  and containing the greatest quantity of detritus, are removed. In the upstream position the mechanical filter  2  previously located downstream is inserted. This filter is most likely less clogged; also nitrifying bacterial flora have developed on it, useful for the removal of toxic nitrogenous compounds. In the opened up downstream position and the middle position two new mechanical filters  2  from the two replacement kits  200  are inserted. 
         [0138]    The new cartridges containing activated carbon  4   a , present in the two replacement kits  200 , are not used at this moment but set aside for future use. 
         [0139]    During a subsequent first waiting period  1300   XL  the filtration unit  1   XL  is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a ,  4   b , i.e. for two weeks. 
         [0140]    In a subsequent second replacement step  1400   XL  the two cartridges containing material for the removal of nitrate and/or phosphate ions  4   b  are replaced by the two cartridges containing activated carbon  4   a  previously set aside. 
         [0141]    During a subsequent second waiting period  1500   XL  the filtration unit is operational for a time period equal to the service period T of the cartridges for chemical filtration  4   a ,  4   b , i.e. for two weeks. 
         [0142]    At the end of this second waiting period  1500   XL , the following steps are cyclically repeated: the first replacement step  1200   XL ; the first waiting phase  1300   XL ; the second replacement step  1400   XL ; and the second waiting phase  1500   XL . 
         [0143]    The filtration methods described above can advantageously make use of an electronic signalization device  300 , possibly integrated into the filtration unit  1   S,M,X,XL , illustrated in  FIG. 11 . 
         [0144]    According to an operation illustrated in  FIG. 12  a first timer  3000  is started when the signalization device  300  is turned on or reset. After four weeks the timer determines the emission of a first signal S 1  corresponding to the first replacement phase  1200   S,M,X,XL  of the methods previously discussed. Upon completion of this replacement a second timer  3100  is triggered that after two weeks determines the emission of a second signal S 2  corresponding to the second replacement phase  1400   S,M,X,XL . Then a third timer  3200  is started that determines the emission of a new first signal S 1  and so on until the device is reset. 
         [0145]    The signals S 1  and S 2  can be optical, acoustic, electric, or other. The signalization device  300  can be connected to a control unit of the filtration unit  1   S,M,X,XL , or possibly integrated inside it. The communication between the control unit and the signalization device  300  can for instance automatically start the timers of the signalization device  300  each time the filtration unit  1   S,M,X,XL  is turned on again after maintenance. 
         [0146]    Obviously a person skilled in the art can apply numerous modifications and variations to the methods and devices described above to meet with specific and contingent needs; these would nevertheless all fall within the scope of protection of the invention as described in the following claims.