I guess the only answer I can give you to that question is that I have never seen a pond where that proposed food chain failed. Have you?

I think the assumption of carrying capacity may be high and that they may not achieve the 18" the scenario proposed. In other words, I think maybe the stocking rate of HSB is too high. The OP has two ponds. Maybe he would like to stock a food chain proposed by you and one by me and then report back in 3,4,5,6,etc years?

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers