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SubscribeNew to CO2 systems
Young Pup
Posts: 233
Kudos: 92
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Registered: 23-Aug-2007
male usa us-indiana
Right now the only plants in my 20 gallon tank are Hornwort and an Amazon sword. I have 1.5 WPG right now, but am going to be upgrading and going to have 2.75 WPG in about 2 months. I decided I'd like to go all out and try to attempt my first real planted tank, so I thought I'd look into getting a CO2 system. I have very little knowledge in this area and was wondering if you guys could recommend a good system for a beginner. I'm willing to spend up to $150 and I was planning on going with a semi-automatic system. Any help is appreciated. Thanks.
Post InfoPosted 10-Jun-2008 00:56Profile PM Edit Report 
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Registered: 28-Dec-2002
male usa us-colorado
EditedEdited by FRANK
First, lets discuss the need for CO2 in a planted aquarium.
Among other elements, plants require carbon.
They get this carbon by breaking down the chemical
bonds holding together the organic compounds
normally found in nature and/or our aquariums.
Fish waste, excess foods, and any dead/dying plant
material all supply these compounds.

Under low, and medium light, some plants are
able to breakdown these bonds and free the carbon fast
enough, with little energy loss, and can grow to
present a beautiful tank.

When we add light, Practically speaking, around the point
where we have 3+ wpg, then we are driving the plants to
faster growth and they cannot break the bonds and use the
carbon fast enough. In this case they will show a growth
spurt, using up stored reserves, and then yellow and die
off. Light has been referred to as the "engine" of plant
growth, and Carbon as the "fuel."

We can accomplish beautiful, lush, green jungles without
adding higher light, or adding carbon, by simply sticking
with low light (.5 - 1.5 wpg) and low light demand plants.
Or, mixing low light plants with medium light (1.5-2 wpg)
To do this we need to discipline ourselves to pass on
many of the plants offered as they require higher light
and more carbon.

Or, we can add carbon to the tank, in a form that plants
can use. That, currently, takes two forms.

We can add a liquid in the form of products such as
Flourish Excel to the tank in the dosage recommended by
the manufacturer.

Another option is the addition of CO2 to the tank.
Normal, ambient, CO2 saturation is around 5mg/l.
To provide the necessary CO2 saturation for the
plant growth we expect we need to increase the CO2
saturation over 15mg/l and most run around 30mg/l
saturation. Over 30mg/l, you run the risk of
stressing the fish. It would be much the same as
being in a submarine with the CO2 Scrubbers not running.
The CO2 saturation would climb and the people (fish) would
not be able to survive.

Supplying CO2 gas can be done three ways.

We can make a DIY CO2 system using an empty 2 liter
plastic soda bottle, adding Brewers Yeast and sugar,
and piping the resultant gas into the aquarium through
hose designed for CO2 gas and a vessel called a reactor
or a diffuser. Using the DIY CO2 generation method is
practical for small tanks. The breaking line seems to
be about 30 gallons. Between 20 and 30G tanks you will
need to have two or more of these 2 liter bottles connected
in parallel to provide enough CO2 gas to make a difference.

Here is one of dozens of sites for DIY CO2 generation:

DIY CO2 generation is messy, can be smelly, and plagued
by frequent leaks. One is constantly washing out bottles
mixing new media, and repairing leaking joints. Sooner
or later folks generally shift to no CO2, or to the
pressurized, bottled gas system.

The bottled gas system, needs a bottle of gas,
a two stage regulator (including a needle valve), a bubble
counter, a one way check valve, and some means of
disbursing the gas in the aquarium - either a diffuser, or
a reactor and some means of constantly measuring the pH
of the tank. By knowing the pH and the KH of the aquarium,
you go to a chart and find the intersection to the two
values and that tells you the CO2 saturation of the tank
in mg/l. When using a chart, simply keep your CO2 Saturation
within the "green", or safe, areas.
This is just one such chart:

The "One way" check valve is installed between the
regulator and the diffuser or the reactor. It allows
the gas to flow from the reguator output through the
valve and into the tank. It's there to prevent backflow
should the bottle run out of gas. It keeps water out of
the regulator.

A more elaborate system uses a computer, called a
"Controller" to constantly monitor the pH, and a shut off
valve to turn the gas on, or off, to maintain a constant
pH and hence, a constant CO2 saturation.

This is but one of many sites, devoted to plants, that
sells bottled gas systems:

Once the gas is piped into the aquarium, you need to
keep the gas in contact with the water so that it can
be absorbed by the water. To do this you would need
either a Diffuser or a Reactor.

A diffuser is used to break the stream of CO2 into
very tiny bubbles. This way the bubbles are so small
that they are moved about the aquarium by water
currents and kept in suspension until they are
either absorbed or they reach the surface and
break escaping into the atmosphere.
Quality diffusers are made of slintered glass and produce
very tiny bubbles.
This is a site that shows, and sells, the better quality

Others use regular airstones, or difusers made of wood.
Regular airstones generally do not produce a fine enough
bubble, and over time the combination of the CO2 and the
water disolve the glue holding the individual grains of
sand together and the "stone" falls apart. The wood difusers
do produce the smaller bubbles but can eventually clog
from bacteria that forms on the surfaces.

A reactor is either external or internal to the aquarium
and keeps the gas in the water until it is all disolved
into the water. I prefer this method as there is no waste.
However reactors are large and the glass diffusers are
very small. It's a matter of choice.

This site also shows the various types of reactors availible.

A third method of generating CO2 gas is the "tablet"
system. You purchase these tablets and when they are
exposed to water, they fizz and give off CO2 gas as they
dissolve. One of these will easily handle your 20G tank.
Here is a site that sells them:

Which way to go....?
Each offers benefits and draw backs.

As I mentioned earlier, the DIY system is limited by the
number of generators necessary, the labor involved in
maintaining it, and frequent leaks.
Another problem with the DIY systm is that you cannot
store the CO2 and release it slowly. The generators
cannot handle large pressures and can explode if the
gas is restricted (metered out). When first started,
the gas surges in quantity and then as the yeast uses
up the sugar and alcohol forms, the gas drops off.
This produces unregulated surges of CO2 gas, and
valleys of little or no gas, much like a sine wave,
which can stress both plants and fish.

The bottled gas system is expensive. But, the parts don't
wear out, and usually barring an accident, don't have to
be replaced. Refilling the tanks of gas is easily done
by taking it to a place that sells CO2 and parts to
bars or to fast food places. In this area they are called
"tap" stores. Refilling my 5 gallon bottle costs me $9
plus tax. Each refill at the rate of 2 bubbles per second
(bps) lasts about 6 months. If I had the controller, it
would last a little longer.

The tablet system, of course requires the purchase of
replacement tablets. I've never run this system so I
have no idea how long "A" tablet lasts.

I hope this helps...

-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--
Post InfoPosted 10-Jun-2008 16:53Profile PM Edit Delete Report 
Posts: 285
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Registered: 13-Mar-2007
australia au-northernterritory
Great post Frank

Can we get this turned into a sticky in either this or the planted board (or both)? The easy to understand info provided would be useful for lots of people considering CO2 systems for their tanks.


Never be afraid to try something new. Remember that a lone amateur built the Ark. A large group of professionals built the Titanic.
Post InfoPosted 10-Jun-2008 17:43Profile PM Edit Delete Report 
Young Pup
Posts: 233
Kudos: 92
Votes: 146
Registered: 23-Aug-2007
male usa us-indiana
Great post Frank, the info was really easy for me to understand.

Like you said, I could just stick with low-light plants and still have a nice planted tank, but I decided I'd like to see if I could pull off a planted tank with a wider variety of plants, and if I run a low-light tank the variety of plants I could keep decreases quite a bit.

I decided that getting a pressurized system would be the way to go, since the CO2 you get from a DIY model isn't consistent and requires constant replacement. I don't know about the tablets, but in the long run it would probably be cheaper to go with the pressurized system.

From what you posted, I'm guessing you run a semi-automatic system, right? Do you think it would be better to go for the automatic or is it not worth the extra cash? Also, is there pressurized CO2 system (semi or fully automatic) that you would recommend I get? Thanks again for all the info.
Post InfoPosted 10-Jun-2008 19:52Profile PM Edit Delete Report 
Posts: 5108
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Registered: 28-Dec-2002
male usa us-colorado
EditedEdited by FRANK
Injecting CO2 with a bottled gas system absolutely
requires the regulator, a bubble counter, and some means
to disburse the gas within the tank (regulator or diffuser).

You need to know your KH, this is relatively stable and
easily adjustable if necessary. Generally just regular
water changes will keep the KH fairly constant. Once
you set your system up, adjust the rate, using a bubble
counter for one bubble per second (1 bps). Either check
your pH every hour for several hours, and match the
reading to the chart to plot the CO2 Saturation. Or,
monitor the pH with a meter and check against the chart.
After say, hour, check again. By this time the injection
at 1 bps and the water circulation within the tank should
have evened things out and you should get a good idea
if, for THAT tank, 1 bps is too little, or too much to
reach somewhere between 15 and 30 mg/l. I'd strive for a
stable 30 mg/l. If you need to adjust the needle valve
on the regulator up or down for 30 mg/l do it, and wait
an hour and check again. If you need readjust again...etc.
Once you have it reading near 30 mg/l, leave things alone
and watch it less frequently, say every 3 or 4 hours.
You will find that the pH will shift when the lights come
on, and plants begin producing O2 instead of CO2 (at night),
Be sure that you peak out at or near 30 mg/l after most
of the day has passed, and then check again during the
night so that you don't over do the injection and stress
the fish. I set my rate of injection so that in the dead
of night, I did not exceed 30 mg/l.

You only need to set the system up once, and make the
major adjustments, and then once a day for a couple of
days continue to fine tune the needle valve, and then
once a week check it. Personally, I did not have that
kind of time between work and other commitments, so I
purchased a pH monitor. Mine is a Pinpoint brand meter.

It runs off a standard 9V battery, and I replace the
battery whenever the display gives me a "low battery"
warning. I know that with my KH and at the set rate
of injection, to have 30 mg/l my monitor should read a
pH of 7.2. Whenever I walk into the room, my eyes
automatically check the monitor and if its reading 7.2
7.1 or 7.3 I know my system is running correctly, and
the saturation is where I want it and where I set it.

Some debate rages back and forth, much like the use of
salt or no salt in a freshwater tank, or carbon, or no
carbon in a freshwater tank, about the use of CO2 24/7.
It is true that during the night, plants shift from
breaking the CO2 molecule apart and using Carbon and
giving off O2, to giving off CO2. "If this is the case
(and it is), then why continue to inject CO2 at night when
the plants are not using it?" Some maintain that the
accumulated CO2 (from the injection and the plants) can
raise the CO2 saturation to dangerous levels.
Others maintain that is becomes a "waste of good gas"
during the nights.

In actuality, for one to raise the saturation that high
you would need either a malfunction of the regulator that
would dump the entire bottle into the tank in a 24 hour
period. Or, you would need your tank so full of fish, that
it resembled a tank in an LFS that housed feeders, and they
just filled it with a new shipment. In-other-words,
super crowded. So, the chances of stressing the fish
through accumulated CO2 is really slim. To double check,
simply view the tank in the morning before the lights come
on. If the fish are all gasping at the surface like a tank
full of feeders, then the saturation is too high and you
should turn down the bubbles per second and immediately
start up an air pump and stick a air stone in the tank
to drive off the CO2 and relieve the fish.

As far as the "waste of gas" comment is concerned, some
turn off the gas at night, and others turn off the gas
and turn on an air pump! If one does this, you drive
the accumulated gas off into the atmosphere, and the
tank plummets to near ambient levels (about 5 mg/l).
Then when the lights come on and the gas is reintroduced,
the tank saturation rises sharply back up to the preset
levels. This can cause a huge swing in pH that could stress
the fish. Turning off the gas at night can conserve
gas but I don't feel it's a necessity, and frankly
the gas is not that expensive. Heck $9 every 5-6 months?

Purchasing a controller, the pH probe and the shut off
valve is probably the most precise way of injecting CO2
gas. It keys on your pH and will maintain the tank's pH
within a gnats hair all day and night. As long as you know
your KH, you know what your CO2 saturation is.

IMO, the decision between fully automatic, or
"semi" automatic, is one of "do you have the extra
cash" or not, and/or if you are a person who has to
have the latest and greatest electronic gizmo.


-->>> The Confidence of Amateurs, is the Envy of Professionals <<<--
Post InfoPosted 11-Jun-2008 01:52Profile PM Edit Delete Report 
Fish Guru
Piranha Bait
Posts: 2511
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Registered: 16-Nov-2003
male canada ca-ontario
Good luck with your plant tank

I don't have my pressurized set up yet, but from what I know a Ph controller alone is past the $150. mark.
For most setups it's also not necessary.

The other part you need for pressurized is a solenoid.
Plug your solenoid into the light timer. Your co2 will follow your light cycle I won't be going for the highest max co2 output, but a mid level as a boost for the plants. This will help avoid large ph swings when the co2 shuts off/on & the co2 will last longer.

Good luck with your plants

The Amazon Nut...
75 & 25g plant tanks.
Post InfoPosted 05-Jul-2010 14:37Profile Homepage PM Edit Delete Report 
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