b_p, Good point. High diveristy with low numbers can work. Crowding and over abundance is usually where the problem lies. Where most pondowners run into problems is when fish reproduce, proper thinning is not done and then overpopulation and over crowding occur which then puts too much pressure on the food resorces.
With numerous species stocked together one or two types seem to reproduce better than the others and their young survive better than the others and then problems start occuring. Probably what helps out Norm is his frequent addition of juvenile predators who keep abundant young fish thinned out.
