I would recommend this :http://de.wikipedia.org/wiki/Paffrathsche_Rinne
The Paffrathsche channel(also: Paffrathsche shell , Paffrathschale )
is a simple device to dissolve (CO2) carbon dioxide in water. Its origin and it most common use is in the aquarium, where it is used for supplying biologically produced ( by yeast fermentation ) CO2. It was named after its developer Kurt Paffrath , an aquarium author. CO2 acts as an important plant nutrient and also affects the pH of the aquarium water .
Principle of operation
An inverted cup , which is mounted, for example by means of suction cups below the water level in the aquarium. In the upwardly facing bottom are often one or two passages assembled , one of the CO2 supply is used and the possible second , provided with a short hose and a shut-off valve is used as a so-called waste gas vent to present in the shell of air , which is lighter than CO2, to let escape upwards .
The supply of CO2 from a fermentation vessel accumulates beneath the inverted bowl . At the contact surface of the resulting CO2 bubble to the aquarium water, the gas diffuses into the liquid. Due to different sizes selected shells there will be differently sized contact or diffusion areas . In this way you can adjust the amount of CO2 to be dissolved on the aquarium size.
Size calculation : Base size : 100 liters
Carbonate contact surfacein
KH up to cm ˛
10 ---> 30
11 ---> 50
12 ---> 70
13 ---> 90
14 ---> 110
15 ---> 130
16 ---> 150
Advantages over conventional CO2 supply devices
Known adding devices (or called reactors) , such as pinball, diffusers or external reactors ( the initiation of CO2 in the water of the filter circuit ) continuously solve the supplied gas in the water. This addition is controlled by controlling the CO2 flow rate.This is in the known pressure bottle systems not a problem because the amount of gas can be set constant by means of a valve .
In biologically produced CO2 , however, the gas generation does not proceed uniformly , it is dependent on the temperature and also on the length of the fermentation process , there is also during production of the CO2 flow, the danger of explosion of the fermentation tank , which is normally only a plastic bottle or canister and is not suitable for high pressure. However, since the contact area of the CO2 to the water in the channel is always the same and there is a more or less uniform addition of the gas is ensured to the aquarium water. If more gas is supplied , as the shell can hold , it escapes just as a bubble on the lower edge of the shell .
Disadvantages compared to conventional CO2 supply devices
Due to the required contact area a Paffrathsche channel inside the aquarium is difficult to hide . The attachment can problematic due to the buoyancy of the gas-filled shell .
For me it worked always well