Actually guys I don't believe it's the numbers one should consider, it's pounds of fish per gallons or cubic feet, and even more specifically how much feed you are throwing into the system. Just recently I had about 1000 yellow perch in a 170 gallon tank before I graded the largest ones out. No problems whatsoever since they were only 2 to 3 inches and I had plenty of biofiltration and aeration. And pound wise the total was quite small.
I've had up to 1/2 pounds per gallon of 7 to 9 inch yellow perch in that same tank with 4 cubic feet of media in a moving bed filter and aeration with no issues. However I was doing a 10 percent water change every day when I got to that point, and cleaning the clarifier at the same time. The tank is circular tank with a center drain with centripetal flow so the settleable solids went to the center drain and were flushed out twice a day via an external standpipe. The suspended solids were sucked into a siphon and trapped in the clarifier. Simple but works great. It would have been even better if the solids were removed right away on a continuous basis such as a rotary drum filter but at this point that is above my pay grade.
Typically if you're not a hard core commercial outfit most literature says not go above 1/4 to 1/2 pound per gallon, and if you do go above 1/2 to 3/4 pound per gallon you will need to use pure oxygen. The big commercial systems that are pushing 2 lbs. per gallon of tilapia have all kinds of back up, and if something does fail they can loose their fish in a matter of minutes. And of course their tanks are self cleaning with solids leaving ASAP.
Last edited by Cecil Baird1; 08/04/14 06:39 PM.
