When i first hit the planted tank scene i got to know a good person of mine his name is George Farmer (www.ukaps.org), he's a article writer for PFK. He's provided some excellent articles that i think you all should take a read over. I give full credit to george and fishforums.net for this article as in no way did i edit, write, or take any credit for it. Hope you enjoy it, as i've read it a million times in my life and have taken alot away from it in my experiences.
Almost half of the physical make-up of a plant is carbon. The vast majority of submerged aquarium plants absorb this carbon through carbon dioxide (CO2) dissolved in the water. There are exceptions i.e. Vallisneria species, that absorb bicarbonates from dissolved minerals in the water, such species therefore thrive in harder water. However, ALL aquarium plants will benefit greatly from adding CO2 to the water.
For those wishing to keep a heavily planted tank, full of lush growth with little or no algae then I consider CO2 addition to be essential. CO2 injection is probably the biggest advance this hobby has ever seen, ranking alongside fluorescent lighting and the recent EI principles.
Why have CO2?
Under low light conditions (generally less than 2 Watts per Gallon) there is normally enough CO2 for the plant to grow successfully without CO2 addition - if a little slowly. If the light levels are increased to over 2 WPG then the plants will grow well for a period until they consume the little CO2 (normal levels are around 4 ppm) that is available in the tank. The plants? growth is then limited by a lack of CO2. The plants will stop growing, inevitably resulting in an algae bloom. Algae?s biggest friend is a tank where there is an abundance of light and little plant growth. It therefore becomes necessary to increase CO2 levels within the aquarium. CO2 addition (injection) is therefore recommended with light levels of 2 WPG or over.
Methods of Injection
The cheapest and a popular way is to DIY. There are many articles available on the Internet so I will not go into too much detail. DIY generally uses an old plastic fizzy drinks bottle with tubing. The bottle is filled with a mixture of sugar, yeast, bi-carbonate of soda and water. The fermentation of the yeast produces CO2. The CO2 goes through the tubing that is normally attached to a diffuser or filter inlet within the tank. The CO2 must be diffused effectively in the water, it cannot just be allowed to escape from the tube directly into the water otherwise the CO2 bubble will just ascend rapidly to the surface and escape into the air.
There are manufactured CO2 systems that work using the same yeast/sugar principles. These are obviously more expensive but have the advantage of being easier to set up and come complete with an effective diffuser. The Nutrafin Natural Plant System is a good example. The manufacturer?s supplied sachets are simply yeast and bi-carbonate of soda. It is worth noting that bi-carb is unnecessary with water that has a GH of 6 or above and KH 4 or above.
One tip is to use more than one unit (DIY or otherwise) to achieve a more stable CO2. This is achieved simply by swapping the mixtures alternately therefore leading to the CO2 level
?peaks and troughs? becoming more evenly spread.
Another more expensive method is the pressurized cylinder. A CO2 filled metal refillable or plastic disposable cylinder is connected to a pressure regulator. This brings down the pressure to usable levels and can be adjusted to achieve the desired flow rate using a needle valve. The CO2 hose is usually connected to a safety check-valve, then possibly to a bubble counter. The CO2 flows finally to a diffuser or reactor. Although initially expensive, these will provide a constant CO2 flow for many months (depending on tank size etc.) They can also be fitted with a night-time shut-off solenoid that is connected to the lights thus saving CO2. This has the additional advantage of reducing pH swings (discussed later). For the ultimate in control a pH controller can be fitted, this will continue to inject CO2 until the pH drops to a preset level. A solenoid will then shut-off the CO2 supply until the pH has risen to the preset level. This provides a very stable pH, ideal for fish and plants. One must be very careful in monitoring the pH sensor (probe), if it accidentally leaves the water then the CO2 may continue to pump away indefinitely possibly killing all the fish.
Yeast-based versus Pressurized
Advantages Cheap, ideal for smaller tanks, easy to set up, little chance of overdosing CO2
Disadvantages Unstable CO2 levels compared with pressurized, high maintenance (changing mixtures, cleaning etc.), little control over CO2 output, not ideal for larger tanks
Advantages Very stable CO2 (particularly with solenoid/pH controller), easily controllable, low maintenance (once set-up will last months generally), ideal for all sizes of aquarium
Disadvantages Expensive initially, possibility of overdosing CO2
Carbon Dioxide Levels and other Water Parameters
Recommended levels of CO2 are 20 to 35ppm. It is important that these levels remain fairly constant, as fluctuating levels are known to cause algae. Higher levels are sometimes used to fight off algae ? it is known that levels higher than 40ppm can block the enzyme production in the algae cells. However one must pay attention to the behaviour of the fish as levels higher than 35ppm are known to cause health issues.
One of the consequences of injecting CO2 into water is that it produces carbonic acid. This acid will reduce pH so it is important that the water has sufficient buffering capacity (Carbonate Hardness or KH). Ideally the water should have a KH of at least 2 degrees or 40ppm.
Measuring CO2 levels is straightforward using accurate pH and KH test kits and reading off the result on a pH / KH / CO2 table. There are many available on the Internet (see my signature). Note that you cannot alter your CO2 levels by simply changing other water parameters. I have known people to use pH buffers with the belief that the lower pH will increase CO2 levels. This seems to make sense if you look at a CO2 table but pH buffers replace KH therefore rendering the reading as useless. pH and KH are intrinsically linked ? it is this fundamental law that allows us to measure CO2.
Another misunderstanding is that low KH results in higher pH swings. This is not true ? see for yourself using a CO2 table, note the actual swing size is identical given the same CO2 levels for any pH/KH. The only issue with low KH is that it may result in a pH crash, however I know of successful planted aquarists (zig for one) that run with KH 1.5 with no problems. I can only assume that if one performs large regular water changes then pH crashes should not be an issue. Perhaps it is the accumulated acids caused by nitrification etc. in a ?less than well-maintained? aquarium that cause the pH crashes more than the low KH alone. Just a thought.
Another benefit of CO2 is that the reduced pH levels can often be beneficial to a lot of tropical fish. The majority of freshwater tropical fish originate from water with soft and acidic water, examples include Tetras, Rasboras, Angelfish, Discus, Barbs, Corydorus, Loaches, Killifish, Gouramis, Bettas and most species of Catfish i.e. Plecs.
During the day (when the tank is lit) the plants take up CO2 and release oxygen (photosynthesis). The take up of CO2 results in a rise in pH with it peaking at ?lights out?. After the lights are off the plants (and fish) take up oxygen and release CO2. This results in the pH dropping reaching its lowest at ?lights on?. If CO2 is continually being injected into the tank through the night then the pH levels will drop further. It is therefore important to test pH levels just before lights on and after lights off to ensure the swing is not too large. Most tanks should not experience too much swing. If the pH does swing by more than one i.e. from pH 7.5 to 6.5 then aeration through the night may be required to drive of excess CO2 or disconnection of the CO2 supply.
Obviously a pressurized system with night shut-off or pH controller would not experience such swings.
Diffusing CO2 into water
CO2 is quite unstable in water and it must remain ?in contact? with the water for it to fully dissolve. Devices that perform this task are commonly known as diffusers or reactors. There are many types of diffusers available ranging from a simple bell-jar, where the CO2 bubbles simply collect and dissolve over time. A more popular method is a ladder-type device where each bubble travels up through a series of ?rungs?, the bubble remains in contact with the water for longer and thus the water absorbs the CO2. This process is visible as the bubbles get smaller as the diffuse into the water. The Nutrafin diffuser is a good example. Other types include a cylindrical type affair where the bubbles rise up a sort of inverted helter-skelter ? the principle is identical. JBL produce such a device. The above diffusers are known as ?self-driven? i.e. the CO2 gas is released into the water with no mechanical drive.
In larger aquariums the common diffusers are not really efficient and another method if diffusion is required. These are commonly known as reactors. They are not self-driven and rely on a source of flow for the CO2 to dissolve effectively. Reactors are normally associated with pressurized CO2.
Common types of reactors are fitted in-line with the external filter output. The CO2 is produced by the pressurized cylinder and flows into the reactor. The reactor is filled with some form of media that allows the CO2 bubbles to dissolve fully where the CO2 enriched water is then pumped into the aquarium.
A really simple method of CO2 reaction is to use the external filter. Personally I run my pressurized CO2 output directly into my external filter inlet. The bubble diffuses through the filter media and the CO2 enriched water flows out into the aquarium. The only disadvantage I can find is the slight noise of the bubble when inside the filter. It is barely audible though, especially if there is any background noise (which invariably there is in my house!)
CO2 and other Nutrient Fertilisation
If one has over 2 WPG of good lighting with a stable CO2 level of 20-35ppm then plant growth will be fairly rapid ? especially if the plants are a fast growing species. The rapid growth results in the plants using up various nutrients (nutrient uptake). These nutrients need to be replenished (preferably BEFORE they run out) otherwise the plants stop growing leading to algae. As discussed algae loves a tank with good light and little or no plant growth.
I would recommend CO2 in ANY planted aquarium, no matter the lighting level.
It is vitally important that one injects CO2 if the lighting levels determines i.e. over 2 WPG (in a standard shape, size tank ? see my lighting article for more detail). Failure to add CO2 to a tank with over 2 WPG will result in algae.
We all want to have a beautiful planted aquarium (I assume that if you are reading this article that you are a planted hobbyist). I believe the easiest way to help achieve this is to inject CO2. If you are starting out with a new set-up then get your CO2 running BEFORE anything else, in particular your lighting. Try to achieve a constant 30ppm