Ok guys here is the information about the yeat thing, i couldnt bother typing it up so i copied it from my previous post.
The Generator
The CO2 generator is simply made from a 2 litre plastic soft-drink bottle. Drill a hole through the lid, force some airline tubing through the hole and seal both sides with silicone sealant. Ensure that this seal is airtight. Alternatively you can drill a hole through a rubber bung (bought from somewhere like Para), force a small-diameter rigid tube (perhaps from an undergravel filter uplift) through, and attach your airline to this. Depending on factors such as the carbonate hardness, number & type of plants, amount of surface agitation, number & size of fish, etc. a 2 litre generator should provide enough CO2 for an aquarium of ( 200 litres. For larger aquariums a larger generator or several generators connected together may be required to produce enough CO2.
The Reactor
The next step is to build a CO2 reactor. The purpose of a reactor is to aid in dissolving the CO2 in the aquarium water. This can be as simple as using an airstone to produce many small bubbles which will dissolve more quickly than a single large bubble.
Another method is to invert a container, place it in your aquarium and allow the CO2 to bubble up and be collected. The CO2 will remain in this container until it diffuses into the water. It probably pays to have a current directed across the opening of the container to constantly bring fresh water in contact with the CO2.
If you have an external canister filter you can feed the CO2 directly into the intake tube. The time it takes the CO2 to exit the filter should ensure it is totally dissolved.
Or alternatively you can mount a wide diameter tube (an old gravel vac is perfect) vertically in the aquarium and feed the outflow of your filter or power head down this tube. Feed the CO2 in from the bottom of the tube and allow it to bubble up against the flow of water thus keeping the bubbles of CO2 suspended while allowing fresh water to constantly mix with and dissolve the CO2. Some fiddling may be necessary to achieve the correct balance between tube diameter and flow rate. If the flow rate is too slow the CO2 will collect at the top of the tube, if the flow is too fast the bubbles will be forced out of the reactor. Additional gravel, foam, bio-media, etc. could also be placed in the tube to impede the upwards flow of the bubbles. A very small vent (such as a needle hole) at the top of the reactor is also advisable to allow any ``extra'' gases such as nitrogen (N2) and oxygen (O2) to escape. The source of these gases can be the original air in the generator which will be displaced by the production of CO2 or if there is a bubble of ``CO2'' in the top of the reactor dissolved gases may come out of solution in an attempt to equalise the concentrations of these gases between the bubble and the water.
There are probably countless variations on these themes. Where possible make reactors out of transparent materials so you can observe the rate at which the CO2 is being produced.
Setting it going
The final step is to prepare the mixture which will produce the CO2. Dissolve 1 cup of sugar (any type of sugar will work) in about 500ml - 1 litre of water and pour into the generator. Dissolve 1/2 - 1tsp. of yeast (bakers yeast is available at any supermarket) in a small amount of warm (NOT HOT) water, add to the generator and top up to the required level with cold water. It is important that you do NOT overfill the generator. Once the yeast is activated and starts to produce CO2 a certain amount of ``froth'' will be produced. Enough head room must be left to ensure that this froth is not forced up the airline and into the aquarium. The addition of 1 tsp. of baking soda will help buffer the mixture and extend its working life. It also reduces the amount of froth produced.
If you use hot water to dissolve the sugar allow the temperature of the mix to reach room temp before connecting the reactor. As this water (and the air above it) cools and contracts it may start a siphon going, dumping aquarium water into the generator, if the production of CO2 has not yet started.
The above quantities are not critical so you can experiment with them if you wish. In general the quantity of yeast controls the rate of CO2 production, and the quantity of sugar controls how long the mix will last. Ideally you want a mixture which will produce CO2 at a steady rate for an extended period of time.
This mix should produce CO2 for at least 20-40 days (often longer). As it takes 12-24 hrs (depending on temperature) for a new mixture to start producing sufficient CO2 it is best to get a new batch started 24hrs before the old batch needs replacing. Alternatively you could have two generators producing CO2, one of which is replaced every week. This latter method probably provides for more stable conditions in your aquarium. The end result of the CO@ reacter is a alcaholic substance at the bottom of the bottle. It smells like wisey and my day had a taste but spit it up because of the bad taste. So dont try it, mabey if you like sniffing wisky then ok.
Heres a picture of my reacter pluges to a small filter. I no longer have it pluged to that as i found it does not disolve the CO2 gas in the water as good. STICK THE TUBE UP THE INTAKE OF A CANISTER FILTER IF YOU WANT GOOD RESULTS, dont
expect anything otherwise.
. 
