Hi mtdewlover, theres many ways to put CO2 into a tank all with pros and cons. Sure the fermentation runs out and you have to replace the mixture, no big deal. Actually if you get two canisters and run them into a single tube then into the reactor you can have constant pressure all the time by staggering the refilling of the canisters. Gas bottled CO2 systems are the choice of professionals and keen hobbyists simply because it works and works well. But there are obviously cons with this method too. You have to take the gas bottle to get refilled, not very often mind you. A 5lb bottle would last you about 6 months. As the pressure in the bottle drops there is a chance should you miss the "end point" the regulator dumps all the remaining CO2 in one go, causing rapid fish deaths. Should any children fiddle with knobs etc there could be disaster too. Gas is great for very keen people who want the fastest growth possible. Another benefit is you can run more than one tank from one bottle. But if you have small kids in the house I wouldn,t recommend them. Another option which is relatively new to the market is the carbo-plus unit. This unit produces CO2 by way of electrolysis, breaking water down into hydrogen, and oxygen. The hydrogen escapes to the atmosphere because its not soluble in water. The oxygen mixes with a carbon sandwich to produce CO2. I have one of these units in a 35 uk gal tank and I get good plant growth and steady CO2 readings. Theres no gas, no canisters no air tubing etc and very safe as it runs at 9 volts in the water. Drawbacks are cost and the sandwich which has to go into the tank is rather big, about 25cmx8cm. The carbon plates are expensive to replace when compared to gas but for convenience this is deffinately the lazy way, great for me!