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.
Reactors
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!)
