Device for purifying water by means of water fleas

Various filters are known for purifying water in an aquarium, a fish pond, a swimming pool or a storage container at a horticultural farm. The device according to the invention contains filtering means at the top of a space in which water fleas are present, which water fleas eat the contaminations (organic waste materials) present in the water and by doing so purify the water indirectly. Said filtering means are necessary because otherwise the water fleas are carried back to the basin along with the purified water. A connecting piece comprising a water lift for transporting purified water extends through the cover of an encasing surrounding said space.

BACKGROUND OF THE INVENTION 
The invention relates to a device for purifying water in a basin, such as 
for example a fishpond or an aquarium, whereby said device comprises a 
box-shaped transparent encasings, which bounds a space in which water 
fleas can be kept in numbers sufficient to purify water which enters said 
encasing via inlet openings, and whereby water exits the device into the 
bassin via an outlet, said outlet being connected to filtering means so as 
to prevent water fleas from being transported into said basin. 
A device of this kind is known from Dutch Patent Application NL-A-9002231. 
In this known device the water to be purified is supplied from the basin 
and is then led to a space where water fleas are present, which water 
fleas extract organic waste materials from the water, as a result of which 
the algae present in the water, which have a negative influence on the 
clarity of the water, are deprived of their food source, as a consequence 
of which they will die and precipitate. The purified water is subsequently 
led back to the basin. 
A drawback of this known device is that any fish eggs present in the basin 
may find their way into said space via the water inlet openings if they 
become detached. Furthermore young (small) fish may find their way into 
said space via the water inlet openings. In that case the water fleas will 
be eaten by the (new) fish after the eggs have hatched, thus reducing the 
effectiveness of the device, which will eventually stop functioning 
altogether. 
A further drawback of the known device is that the water fleas may leave 
said space, especially at night, thus reducing the effectiveness of the 
device. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a device which does not have the 
above drawbacks. One object is to provide a device which effectively 
fights algae. To that end a device according to the invention is 
characterized in that the device includes a cover with an edge at the 
upper side of the encasing, in that the filtering means are present at the 
top of said encasing, in that said filtering means are connected to the 
outlet of the device via a connecting piece, and in that said inlet are 
provided in a number of places between said edge of said cover and said 
encasing. 
The invention is based on the perception that when the filtering means are 
placed at the top of the space rather than at the bottom, the water fleas 
will be unable to leave said space. The construction of the cover 
furthermore renders it impossible that the eggs find their way into the 
space via the inlet openings. 
One embodiment of the device according to the invention is characterized in 
that said connecting piece comprises a water lift for transporting 
purified water. 
One embodiment of a device according to the invention is characterized in 
that said cover comprises an additional protective edge for closing said 
space to fish eggs.

DETAILED DESCRIPTION OF THE INVENTION 
The FIGURE shows an embodiment of a device 1 for purifying water in a 
basin, such as for example a fishpond, an aquarium, a swimming pool or the 
water supply at a horticultural farm. 
The device comprises a box-shaped, for example cylindrical, encasing 3 made 
of a transparent material, such as glass, plastic or a transparent plastic 
material (for example PET). The encasing 3 comprises a space 5, in which 
filtering means 7 are placed. Said filtering means separate a space 9 from 
space 5. When the device is in use water fleas are present within space 5, 
said water fleas being unable to reach space 5 because of the presence of 
the filtering means 7. The encasing 3 is closed by a cover 11 at its upper 
side. An opening 13 is provided in (for example) the centre of said cover. 
A tubular connecting piece 15 is placed in said opening. Said connecting 
piece includes a first end 17, on which an outlet 19 is placed. Said 
outlet preferably makes a bend (for example 90.degree.) in order to 
achieve the desired water circulation. A tubular portion 23 of a filter 
holder 25 is slid over the other end 21 of connecting piece 17. At its 
other side 27 the filter holder includes a funnel-shaped end. The 
filtering means are slid into or over the end of said funnel and clamped 
down therein or thereon. 
Connecting piece 15 furthermore includes a tubular inlet 29, which inlet 
may be connected to an air pump. After the filter holder 25 has been 
mounted on connecting piece 15, the air can move downward, via tubular 
inlet 29 and then via a channel 31 defined by tubular portion 24 and 
connecting piece 15, and subsequently upward in connecting piece 15 (via a 
so-called water lift) to end 21 and finally, via end 17 and outlet 19, to 
the basin. 
While rising in connecting piece 15 the air bubbles carry along water, as a 
result of which water is discharged from space 9. The amount of water that 
has been discharged is replenished again from space 5. Small openings are 
provided in a number of places between edge 33 of cover 11 and the 
encasing 3, so as to enable said replenishing of water in space 5. As a 
result of this water can pass between parts 35 and 37, over the encasing, 
into space 5. The water flow entering space 5 via said inlet openings is 
so strong that the water fleas cannot escape via said openings, either. A 
portion 39 screens off the edge of encasing 3. Instead of connecting an 
air pump (to 29) it is also possible to connect a water pump to outlet 19, 
as a result of which the water is sucked out of the space through filter 
holder 25. In that case tubular inlet 29 must be closed. 
In practice the water fleas appear to thrive in the water (in which algae 
and organic waste materials, for example from fish, are present), and they 
appear to purify the water to such a degree that the water exiting the 
device via outlet 19 has been rid of organic waste materials. Thus the 
basin no longer contains any food for the algae. As a result of this the 
algae will die and precipitate, and the water in the basin will become 
clear and remain so. 
The device appears to function quite satisfactorily in practice, whilst in 
addition it is of simple design. 
Once the device has been commissioned, the filtering means 7 may become 
silted up during the initial period. In order to clean the filtering means 
connecting piece 15 with filter holder 25 and filtering means 7 is lifted, 
turned forward and backward a few turns and then returned to its original 
position. Said cleaning is only necessary during the initial period after 
the device has been installed, because mosquito larvae will settle on 
filtering means 7 after some time, and once settled they will graze the 
filtering means clean, especially once they are fully grown. 
The only maintenance which the device furthermore requires is occasional 
cleaning of the outside of the encasing. This is necessary because the 
water fleas need daylight. The amount of water fleas in space 5 is 
adjusted in a natural manner in dependence on the amount of waste 
materials and algae in the water. 
The so-called water lift (29, 31, 21) can vent (the system) at the time of 
the installation in that the entire unit is lifted and maintained in that 
position until the air has been removed from the space.