From: tli@caldera.usc.edu (Tony Li)
Newsgroups: alt.aquaria,rec.aquaria,sci.aquaria
Subject: FAQ: Plants
Date: 1 Sep 1992 01:05:10 -0700
Organization: University of Southern California, Los Angeles, CA
Expires: 30 Sep 1992 08:05:01 GMT
Reply-To: tli@cisco.com,patti@hosehead.hf.intel.com
NNTP-Posting-Host: caldera.usc.edu

				  Plants

Rev. 1.7 8/21/92

Prologue:
---------
This monthly series is intended to address some of the frequently
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the answers may not be complete, please feel free to ask questions. 
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topics. 

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with "(FAQ)" in the subject line.  You are absolutely welcomed to tackle
(i.e. WRITE) sections that have not been written yet.

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CO2 in the aquarium
-------------------
     Anyone who has observed the explosive growth of aquarium plants in
response to carbon dioxide (CO2) fertilization must be convinced of the
usefulness of this system.  Certainly, there are thousands of aquarium
hobbyists who do not give their plants any sort of special treatment and
still end up with a fairly nice display.  However, truly luxuriant
growth, the sort that you see on the covers of aquarium magazines and in
pictures of "Dutch aquariums," can only be achieved by fertilizing with
CO2.
     During photosynthesis, plants use light energy to capture CO2.  This
CO2 is used to build the basic carbon structures from which all plant
material is made.  In a poorly lit aquarium, light is likely to be what
limits the rate of plant growth.  The amount of CO2 produced by fish- and
bacterial respiration is more than enough to allow photosynthesis under
these conditions.  If on the other hand, you try to make your plants grow
faster by adding more light, it is likely that there will not be enought
CO2 in your aquarium.  The plants simply can not grow as fast as they
would like to, given the available light energy.
     The easiest way to increase the amount of CO2 in an aquarium is to
buy a tank of CO2 and let it bubble into the water.  Several, mostly
German, companies sell systems for adding CO2 into the outflow of your
canister filter.  If you buy your CO2 system from someone like Dupla, you
are likely to spend about $300.  That seems a bit pricey, doesn't it?
Fortunately, it is very easy and also a fair bit cheaper to buy a CO2
tank at a local welding supply place and use it to bubble CO2 into the
water.
     The general system is illustrated in the accompanying figure.  CO2
in the tank is under high pressure.  A pressure regulator brings this
pressure down to a manageable level, and ordinary aquarium air valves can
be used to regulate the flow to individual aquariums.  The CO2 reactor is
simply a small chamber that allows the CO2 to be dissolved in the water
before it escapes into the air.  Outflow from a filter or a pump enters
the top of the reactor; CO2 is bubbled in from the bottom.  To give the
CO2 more time to dissolve, one can add a system of baffles to trap the
gas as it is moving up.  Near the top of the reactor, there should be a
small hole to vent other gasses, which may be present in small amounts in
the compressed CO2.  These gasses do not dissolve as readily in water as
CO2 does.
     I purchased my CO2 tank and regulator at Wesco on Vassar Street in
Cambridge.  Their current (May 1992) prices are: 5 lbs CO2, $52.50, refill
$9.74; 20 lbs CO2, $101.75, refill $19.55.  A CO2 pressure regulator is
"$79 and change."  People who have better welding connections than I do
might be able to get things more cheaply than that.  Refills are
generally not a very big expense.  My 20 lb CO2 tank is used on three
aquariums (30, 65, and 110 gallons) and lasts about three years between
refills.  That works out to about $2 per aquarium per year.  Other
possible sources of CO2 that I have not investigated are CO2 fire
extinguishers and the CO2 canisters they use to but the bubbles in beer
and soft drinks.  Don't bother trying to rig up something with dry ice,
it is too complicated.
     The tubing and valves that I use for my CO2 setup are the sort that
one buys for use with the aquarium air pumps.  It is better to get the
brass rather than the plastic valves, since it is easier to make fine
adjustments with them and they also tend to leak less.  Even a tiny leak
can empty out a gas tank distressingly quickly.  I check all of my valves
and connections with a soap solution and make sure that no bubbles
appear.
     The CO2 reactor can easily be constructed out of any wide bore tube.
I use the lift tubes from an undergravel filter in my aquariums.  Local
aquarium enthusiast Jim Bardwell does well with the top half of a
one-liter coke bottle, with the filter hose attached to where the cap
should be.  It is best to use a clear plastic, so that one can see what
is happening inside.  Baffles, designed to let the water cascade down in
one direction and to trap the CO2 moving in the other direction, are
helpful, but not absolutely necessary.  I make my baffles out of foam
cubes that I cut to the right size and shape to fit inside the tube.  Jim
simply lets the CO2 collect at the top of the reactor, where the water is
coming in.  He does not have a vent and does not seem to have a problem
with excess gas accumulating.
     While a small increase in the amount of CO2 in the water causes lush
plant growth, too much CO2 can prove to be toxic.  CO2 dissolved in water
forms carbonic acid (H2CO3).  With weakly buffered water, like what comes
out of the tap in the Boston area, adding too much CO2 can bring the pH
down to as low as 3.  That is not quite as acidic as Coca Cola, but about
equal to vinegar.  Naturally, this can cause death or other serious
reactions in your fish and plants.
     One can buy CO2 test kits that measure the actual level of CO2 in
the water, but measuring the pH and counting the bubbles in the CO2
reactor works just about as well.  It is best to start off by adding CO2
very slowly (about one to three bubbles per minute) and increasing the
rate until a small, but measurable drop in pH is achieved.  In my
30-gallon aquarium, I add one bubble of CO2 every three to four seconds
to bring the pH from 7 to between 6 and 6.5.  How much CO2 one needs to
add varies from aquarium to aquarium and can depend on several factors:
the size of the aquarium, how fast the plants are growing, the number of
fish, how much food is decaying on the bottom, the buffering capacity of
the water, the types of rock and gravel, and how well ventilated the
surface of the water is.  However, anything in the range of one bubble
every two to fifteen seconds seems to work pretty well.  Bubble size will
vary with the diameter of the tubing.  I am referring to the sort of
bubbles that come out of the end of ordinary, one eighth inch inside
diameter aquarium air tubing.
     By using a CO2 reactor, you are saturating the water with CO2, and
any excessive agitation of the water surface or bubbling of air through
the water will cause the CO2 to escape into the atmosphere, just about as
quickly as you can add it.  Thus, at least during the day, you should
*not* have an airstone or an undergravel filter turned on.  If you have a
plant aquarium, you should probably not be using an undergravel filter,
anyway, since most kinds of plants do better without one.
     When the lights are on, plants use CO2 and produce oxygen.  In my
tanks, so much oxygen is being produced, that I can often see it forming
streams of bubbles from the plants.  At night, on the other hand, the plants 
are actually using oxygen (and not CO2)  If there are not too many fish in 
the aquarium, then the oxygen produced by the plants during the day will 
tide everyone over until the next morning.  However, if you notice that you 
fish are gasping at the surface in the mornings, they are obviously running 
out of oxygen.  To remedy this problem, you can simply turn on an air
stone when the lights go out.  This will keep up the oxygen level and
remove excess CO2.  I have the aquarium lights and an air pump on two
separate timers; when one turns on, the other one turns off.  It would
also be fairly easy to rig up a solenoid valve for the CO2 supply and
have it turn the CO2 on and off with the same timer that is regulating
the lights.
     The system that I have described here and use is a very basic one
that works well.  For those who like those sorts of things, the
automation possibilities are almost limitless.  My brother Albrecht, who
is an electronics whiz, has his entire aquarium run be a TRS-80 computer.
Among many other things, the computer measures the pH, adds more CO2 if
the pH is above a predetermined level, and sounds an alarm if the CO2
tank is running low.  Fortunately, you don't need all of that to have a
truly great-looking plant tank.  There are more than thirty kinds of
thriving plants in my aquariums;  I have to weed out bunches once a week,
and I have enough extras to supply all of my aquarium friends and still
sell some at the monthly BAS auction.  The fish are also doing well and
reproducing.
     CO2 makes it easy to grow aquarium plants, but it is not a cure-all.
You still have to observe some of the other essentials of proper plant
care.  Aquarium plants need a lot of light.  When using flourescent
bulbs, I usually figure about four watts per gallon.  Wide-spectrum plant
and aquarium bulbs seem to work better than the "soft white" ones that you
can buy at the hardware store.  The amount of iron in most aquariums is
too low for maximum plant growth.  I supplement the iron by adding
"Micronized Iron" to the canister filter (about one teaspoon at every
cleaning) and "Ortho Greenol" directly to the water (two drops per ten
gallons per day).  Both of these are available at gardening stores.
Other nutrients and trace elements that your plants need are usually
taken care of when you feed the fish and do water changes (frequently).
Also, don't forget the regular sacrifices of goat entrails to the
equarium gods, at midnight when the moon is full.
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