I have about 12 in a 50 breeder, Fry all the time. I have about 20 in a 120 tank and fry all the time, About 15 in a 55 and fry all the time. I do water about every 3or 4 days and never on time, Some times i'll do a tank and if i'm there a day later i'll take out some. Two gal some more some less. The guys above me have good thing to keep in mine also.