Depends on several things, are you controlling the temp? Are you using Micro aeration stones? How often are you cleaning the tank, and with what? What seasonal maximum are you holding; in early spring you can hold 1/4th more at max than during the heat of summer (July, August). Are you feeding them, and if so what kind of filtration are you running? Lastly, how often are you refreshing the tank? Nitrogen build up and ammonia build up will be 2 of your biggest problems besides temperature controll...worked in a bait shop, we changed the tank out 2/3rds every 3 days, and used an Artica chiller, heat of summer we could keep 9 pds of fathead minnows max without excessive die offs if the tank was kept clean and was refreshed on a regular basis...