4.9.1 MANUAL ADDITION OF CO2:

To install a manual carbon dioxide setup you will require the following items (minimum suggested configuration, Thiel 1985):

• a canister filled with CO2. Can be bought in 2.5, 5, 10 and 20 pound canisters, and larger sizes if you acquire an industrial 55 pound or greater unit. Make sure that the canister you buy carries a DOT stamp or you will have great difficulty in having it refilled. It is often illegal to refill bottles that do not carry such a stamp.
• a set of CO2 gauges, preferably coupled with a pressure reducing valve.

These are highly recommended because the pressure in a CO2 bottle is over 800 PSI. If you do not reduce the pressure first, you will have great difficulty in adjusting the output going to the diffusion system. It is a good idea to get gauges that are U.L. listed, and American made, to ensure that the threads on the bottle and the threads on the gauges match properly.

• CO2 resistant hose (should be silicone hose or flexible PVC hose, sometimes called Tygon, one of its brand names). Regular airline tubing type hose hardens quickly when put in contact with carbon dioxide and will crack, causing you to loose CO2 and resulting in your canister being empty frequently for no apparent reason, making you wonder why it only lasts a few days.
• one or more check valves that are CO2 resistant. One is the minimum. Two is better. They prevent water from backing up in the CO2 line and entering your gauges, shortening their life, or ruining them altogether.
• a CO2 diffusion system (reactor, or other device to mix the carbon dioxide and the water efficiently). The more efficient the diffusion setup, the less CO2 you will be using, and the longer your canister will last.

And a highly recommended option:

• a solenoid (magnetic valve) to shut off the CO2 supply at night.

The hook-up procedure is as follows:

• Measure the pH and the carbonate hardness of the tank that you are planning to add carbon dioxide to. If the pH is too low already, you cannot add CO2 now. A pH below 8.1 is too low for the purpose of adding carbon dioxide. You must first adjust it. In all likelihood, if the pH is low, the carbonate hardness will be low too.
• Adjusting the KH (carbonate hardness) is necessary because it protects the tank from acid fall. When CO2 is added to the tank's water, a weak acid called carbonic acid is formed. This acid will lower the pH of the water quickly, unless the KH is high. Levels of dKH 12 and higher are recommended (4.3 meq/l and higher). To adjust the KH level, use a liquid or powdered buffering compound. Make sure it does not contain binders, or your protein skimmer will overflow after you add it to the water. Make sure, too, that it does not contain phosphate based compounds, or you will have problems with micro-algae soon after using the compound.
• Raise the KH level slowly. Do not increase it by more than 1 dKH degree per 12-24 hour period (dKH stands for German degrees of hardness). Although formulas for homemade hardness generators are described in several books, be careful when using them. Most hobbyists do not have access to the carbonate part and, as a result, only use the bicarbonate part usually in the form of baking soda. Such is very dangerous as it will raise the pH of the tank to dangerous levels and make it very difficult for you to bring it back down to the correct range. Additionally, adding too much sodium bicarbonate (baking soda) will quickly raise your pH to a level that cannot be sustained safely in the aquarium for long periods of time.
• Make sure the canister of CO2 bottle is full and closed. Attach the gauges to the CO2 bottle (canister). Do not open the bottle yet. If you are using one, hook the solenoid up to the gauges. Run a short length of CO2 resistant hose from the gauges, respectively solenoid, and insert a check valve. Run another foot of hose and install the second check valve (if you are using two). Now run hose from the output side of the check valve to the input of the diffusion system that you are using.
• The solenoid (magnetic valve) must be plugged in to a 110 volt power source. If you are using a timer (which is strongly suggested), plug the solenoid into the timer, and the timer into an outlet. Run the magnetic valve (normally closed type) for the same number of hours as the lights. Alternatively, plug the solenoid into the same timer as the one that controls the lights, if such can be done. The reason for this is simple: during the night, when metabolism is low, and when photosynthesis is not taking place because the lights are off, algae add CO2 to the water themselves, rather than removing it. Moreover, during the night less carbon dioxide is required to begin with. Such a hook-up will also prolong the useful life of your CO2 canister refills.
• Start by opening the bottle completely, making sure first that the solenoid is not plugged into an electrical outlet (or into a timer that is energized). Since it is not plugged in, it will be closed, and will not let any carbon dioxide go through.
• Adjust the pressure reducer to a pressure of around 1 to 2 psi. If you are not using a pressure reducing gauge you cannot follow these directions because you will not be able to adjust the pressure of the CO2 coming out of the canister.
• Let the CO2 go into the diffusion system, together with the water with which it will mix. Follow the directions for setting up your diffuser carefully. If you are unsure, call the store you bought it from, or the manufacturer to get an explanation over the phone.
• Because of the back pressure exerted by the water going into the diffuser, 1 to 2 psi may not be enough pressure for the CO2 to get through, and mix with the water. If such is the case, increase the pressure gently until CO2 does get into the diffuser and mixes with the water.
• Optional: use a bubble counter to determine how much CO2 is actually going into the diffuser. This is a small device that is hooked up in-line with the CO2 line and allows you to actually see how much is going into the diffusing device.
• You should only let very little CO2 get into the diffuser when you first start the system up. The reason is that you do not know yet what its effect is on the water. As a result you want only little CO2 to mix with the water until you can actually test what is happening. If you can determine how much is actually entering the diffusing device, for example because you are using a bubble counter (a small device that lets you see how many bubbles of CO2 past through the lines), adjust the system to push about 45 bubbles per minute through the CO2 line. If you are not using such a device, adjust CO2 output for its minimum.
• In a 55 gallon aquarium let the system run for about 4 to 5 minutes, on average, (less in smaller tanks, more in larger tanks).
• Now stop the output by closing the CO2 canister shut off valve. Do not adjust the pressure gauge, such is not necessary. Moreover, you probably spent quite some time to adjust it to the correct level.
• Now test the pH of the water again and compare it with the first reading you obtained, the one from the test before you started adding carbon dioxide.

The following three scenarios can now occur:

• If the pH has not varied increase the output of the CO2 line a little, for example to 60 bubbles a minute, or slightly more than before if you are not using a bubble counter. Wait a few minutes and test again. Keep doing so until the pH has fallen by a minimum of 0.1 pH to a maximum of

• The pH has gone down. The drop is between 0.1 and 0.2 pH. Leave the settings as they are. This is the correct level of diffusion.
• The pH has dropped more than 0.2 pH, for example from 8.2 to 7.9 pH. You are adding too much CO2 and you must reduce the CO2 amount that you are dispensing even further. In all likelihood your carbonate hardness is still low, probably below 12 dKH. Check it and adjust it, if necessary.

The key when using carbon dioxide is to understand right from the beginning that it is a process that you need to understand and have control over. Carbon dioxide lowers the pH and if you dispense too much of it, especially if your carbonate hardness is below dKH 12, the pH will drop drastically, quickly, and perhaps to a dangerous level if that too strong diffusion goes on for too long.

Carbon dioxide diffusion is not a dangerous process at all, as long as you know what you are doing, and take the time to make the adjustments. Do not walk away from your system while you are setting up a carbon dioxide system. Stay around until the diffusion procedure is completed. Does not kill fish, as you sometimes will hear. You must, however, take care that both the dKH are correct and that the amount dispensed is not lowering the pH by more than 0.2 pH.

After the CO2 system is up and running, two water quality checks need to made from time to time:

• The pH drop should never be more than 0.2 pH from the first reading you took.
• The dKH needs to be checked at least once a week, preferably twice, and needs to be adjusted upwards whenever necessary, using a KH generating liquid or powder. Keep the remarks made earlier about such compounds in mind.

Once you start using CO2, you must ensure that you have a continuous supply available. Check your bottle (canister) regularly and locate a source for refilling it, in advance. Do not wait to do so until it is empty. If you own a bottle with a D.O.T. stamp, just about any welding supply place will be able to help you.

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