Place a small tank in a place where it will get some light but is well protected. Make a solution of three packets yeast, two tablespoons flour, and enough water to fill tank well mixed. Place in tank and add culture, an air stone, a good cover, and a heater if needed.
Once a week strain off half the water from the top of the tank with a coffee maker filter and feed filtrate to fish.
Mix a volume of water equal to that taken out with two tablespoons flour and return to tank. Do not add sugar as yeast will "bloom" and contaminate tank. There is plenty of sugar in the waste from the paramecia and the flour to keep the yeast going and the paramecia live just fine off the yeast.
If your protein is high in your fry tank the intermediate sugars from protein decay may spark a yeast "bloom". As long as the water is diluted out before alcohol levels can rise there is no problem. Do a forty percent water change and the fry should be able to control yeast. If problem persists do another change, and if a third is required it is a wonder your fry survived in that nasty water.
Article copyright ©2001 by Larry Rogers, all rights reserved.