Thank you for the comments, Anthropic.
Sorry to belabor this. I have one additional comment on Physical Chemistry and ponds. A pond is like a chemical reaction between organic molecules. The outcome is almost never 100% of the desired product but a series of products and side products with their own Gibbs free energy (remember, deltaG=deltaH-TdeltaS - I don’t know how to put in greek characters here)
->E+F y% etc.
Why? Because we are talking about an ensemble of molecules each with their own kinetic & rotational energy and each bond with its own vibrational energy and each electron in their own excited state - nothing is at rest. The result is often temperature dependent, concentration dependent (think oxygen) and scavenger dependent (eg. free radical scavengers in chain reactions). Yields of the desired product are seldom over 70%. Is this an analogy for a pond?
When it comes to fish food, we see a very similar process. Our desire is for maximum gain of healthy weight, minimal waste product. But even when the fish eat every pellet so none just goes to the bottom & decays, they can only retain so many proteins & nutrients. We're doing well if 100 lb of feed creates more than 50 lb gain of weight. Too much fat can shorten life, as well.
This is much better weight gain than from natural food like insects & small fish, however. Fish must chase them down, using up energy, and besides they are mostly water.