Have you considering netting off a section of the pond where you can grow out those 4000 1-3" CNBG?

If you did so, then you could feed them Aquamax Grower, or similar, and get them to 5" pretty quick.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."