For larvae control (what I use) consider Microbe-Lift/BMC, "Biological Mosquito Control," a very concentrated 8% Bt toxins liquid. With this sold for killing larvae in ponds and bodies of water, the labeling is:
Recommended application: 2.5 ml (measuring cup provided) per 1,000 gallons of water every other week. 6 oz for ponds up to 5,000 gallons.
This is equivalent to .0025 ml or 2.5 microliters/L, and this is for as needed use, not constant use as we would use this product. I add 1 drop or more on average for every gallon or 2 of feed. Even at that very high dose, just a 2 oz. dropper bottle is seeming going to last at least a year. It's cost, such as 6 oz. for <$20 with free shipping, even if used at needlessly high doses, is negligible; and it definitely works for me. With your high-end automated feeding setups, I would think you'd prefer to simply add drops or a squirt of a liquid Bt product vs. relying on ground-up mosquito dunks.