Carbon Dioxide (CO2) Plants are made up of 50% carbon (dry weight). Submerged aquarium plants absorb carbon through carbon dioxide (CO2) dissolved in the water. All aquarium plants will benefit greatly from adding CO2 to the water. For those wanting to keep a heavily planted tank, full of lush growth with little or no algae then I consider CO2 addition to be almost essential. 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 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 6ppm) that is available in the tank. The plants growth is then limited by a lack of CO2. The plants will stop growing, resulting in an algae bloom because of the light and suspended nutrients. Algaeâ€™s biggest friend is a tank where there is lots 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. The high lighting â€˜drivesâ€™ the plants to uptake more CO2 and nutrients (see Lighting article). METHODS OF INJECTION Yeast-Based The cheapest and a popular way is to DIY. DIY generally uses an old plastic fizzy drinks bottle with tubing. The bottle is filled with a mixture of sugar, yeast, water and bi-carbonate of soda. The fermentation of the yeast produces CO2. The CO2 goes through the tubing that is normally attached to a diffuser or under the 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 rise to the surface out of the water. Here is a guide on how to build a DIY CO2 system: http://www.fishforever.co.uk/carbondioxide.html http://www.aquatic-eden.com/2006/10/bui ... rator.html There are manufactured CO2 systems that work using the same fermentation process. These are slightly 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 manufacturerâ€™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. I would recommend to use more than one unit (DIY or manufacturer system) to achieve a more stable CO2. This is achieved simply by swapping the mixtures alternately, one at the weekend and one midweek. Also I would chuck the mixture supplied with the Nutrafin system as the yeast is produced to last longer than normal unlike bakerâ€™s yeast. Another option is to use brewerâ€™s yeast which can support a higher alcohol content so therefore lasting even longer. Pressurized Cylinder 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 can be connected to a solenoid which can be timed to turn off at night to save CO2 as plants donâ€™t use CO2 at night. It also stops the ph dropping to low which could be fatal to your fish (more on this later). Then to a bubble counter (BC). The BC counts the bubbles produced per second (BPS) or per minute (BPM).A safety check valve is fitted to ensure no backflow of the aquarium water goes into the solenoid or Gas canister. Finally the CO2 flows to a diffuser or reactor. Initially these are expensive, these will provide a constant CO2 flow for many months (depending on tank size, planting density etc). 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. However, the downsides to pH controllers far outweigh the advantages of a stable pH (which isnt actually necassary in itself!). CO2 injection will drop the pH by approximatley 1 unit - fish experience pH swings much larger than this in the wild, one example is acid rain. Also, the CO2 being switched on and off constantly causes instability which may lead to algae problems. Finally, a pH controller may actually limit carbon to the plants. For example, you decide you dont want the pH to drop below pH6.5, and your tap water is pH7. Before you can inject 30ppm of CO2, the pH controller will cut it off due to the pH being to low!! you may only be able to inject 20ppm in that time period. Liquid Carbon Becoming increasingly popular is liquid carbon. It isnt actually carbon, but a complex carbon compund made up of glutaraldehyde (C5H8O2) as a base foundation, this goes though various chemical proccesses and it is fixed into carbon using the calvin cylce. Liveworts, Bladderworts & algae do not have this function, so instead it becomes toxic to them. most plants are fine with the reccomended dose, but then they rot if they are raised. Particular species include: vallisneria riccia fluitans utricularia graminifolia egeri densa Liquid carbon is an excellent alternative to other CO2 methods, but it is worth mentioning it isnt as effective as CO2 gas alone. It can be dosed alongside other types of CO2 injection methods. It is very cost effective on small tanks. Yeast is Cheap to set up, but may cost as much or more in the long run, it is ideal for smaller tanks and easy to set up. There is also little chance of overdosing CO2. Some disadvantages of yeast based system is that there is unstable CO2 levels compared with pressurized which could cause algae, there is high maintenance (changing mixtures, cleaning etc.) and little control over CO2 output, not ideal for larger tanks as lots of bottles are needed. With pressurized, you get very stable CO2 (especially with a solenoid), it is easily controllable, it is low maintenance (once set-up it will last months depending on size of tank and plant mass), it is ideal for all sizes of aquarium, no matter what size, whether it be 1 or 1000gallons. It is expensive initially but cheaper over the long run and there is a possibility of overdosing CO2 but it is easily adjusted to bring it under control. Once the pressurized system is set up, the pressure may drop so it may need tweaking a little but it should be rectified within 48 hours. You can also do a DIY pressurized system, as long as you leave the safety pin in, dont press the handle, and don't knock it over then everything is ok. Fire Extinghuisher CO2 Courtesy of Sam (themuleous) for writing this excellent Guide. LEVELS OF CO2 IN THE AQUARIUM Recommended levels of CO2 are 25 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 you must watch the behaviour of your fish high levels can cause problems. One of the consequences of injecting CO2 into water is that it produces carbonic acid. This acid will reduce pH (generally by 1 on the pH scale) 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. However, people have reported no problems even when using 0dKh water!! using pH/ KH relationship charts is a very innacurate way of measuring CO2 levels. Tank water contains other acidic substances, which can affect the reading. Even Nitrate and Phosphate can! As the CO2 gasses off from the aquarium into the drop checker, the ph lowers due to the carbonic acids formed by CO2 when it dissolves in water. When the drop checker turns from blue, to green, this indicates a pH of 6.6, and because we know the solution is 4dkh, this tells us we have approximately 30ppm of CO2 in our tank water. If you are using a 5dkh reference solution, then a pH 6.6 (green drop checker) will indicate 38ppm. Another way of measuring CO2 is to use a drop checker (DC), You fill the ball with 4DKH solution (make it yourself or get it from Aqua Essentials ) You then add a couple of drops of bromothymol blue or low range pH test to the 4DKH solution. This should then turn blue. Turn it the correct way up and place in the aquarium, the air bubble (forms automatically) will stop the solution mixing with the tank water. CO2 measurment usng a Drop Checker A 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. Blue - low CO2 (less then 20ppm) Green - Ok (between 20ppm & 35ppm) yellow - too much (over 35ppm) PH SWINGS During the day (when the tank is lit) the continuous injection of CO2 causes the pH to drop as carbonic acid is produced. we usually use a solenoid to cut the CO2 off at night, which means the pH would then rise as the CO2 gasses off, but if you dont, then the pH will remain fairly constant. Injecting CO2 usually causes a drop in pH by 1 unit. DIFFUSING CO2 INTO THE WATER CO2 is quite unstable in water and it must remain in contact with the water for it to fully dissolve. There are devices that help with this and these are called 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 the water absorbs the CO2. This process is visible as the bubbles get smaller as the diffuse into the water. The Nutrafin kit comes with a ladder diffuser. In larger aquariums the common diffusers are not really efficient and another method is the reactor. 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; you can run the CO2 output directly into your external filter inlet. The bubble diffuses through the filter media and the CO2 enriched water flows out into the aquarium. The only disadvantage is that it can make a slight noise when inside the filter. It is still quiet though. CO2 AND OTHER NUTRIENT FERTILISATION If you have over 2 WPG of 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 (particularly stem plants). The rapid growth results in the plants using up various and more nutrients. These nutrients need to be replenished by a fertiliser; otherwise the plants stop growing leading to algae. Therefore fertilisers need to be added regularly. EI using dry salts Injecting CO2 in an aquarium no matter how much light you have will help, even low CO2 is better than no CO2. Please ask for specifc information on your tank in the planted section.