There are no solutions, only tradeoffs. That's why I like observational evidence to verify theories & models of complex phenomena.
Where you are wrong Frank is that there is no verification of theories ... only falsification. No such thing as evidence of or proof of theoretical ideas. Matter conservation is theoretical principal that has never been falsified yet never proven.
The advantage to the approach that I offered for quantifying the wastes as a practical method of budgeting and tracking nutrient addition is that it relies on more reliable evidence. The evidence of dry matter gain which is much better metric that is more easily measured than waste. Aside from the obvious problems of collecting pooh ... a fair percentage of the waste is in molecular form. For example, some of the protein fuels the process of assimilation and upon extracting the energy the byproducts of CO2 and ammonia are released in molecular form. These are in solution and would have to be measured independently and are not in the pooh at all. In daylight, the CO2 is rapidly scavenged but the ammonia can persist. Anyways, relying on the metric (EVIDENCE) of FCR and the nutrients proportions most commonly EVIDENT for a species is a very practical estimate with acceptable uncertainty. That there is uncertainty is immaterial as an argument against a solution or method. My example suggests a range of 18% to 22% assimilation. Anyone who would argue for example that this uncertainty invalidates the range of expectations is just obstructing an appropriate application of EVIDENCE. Anyone who might suggest the lack of measurement in the estimate claiming, for example, that the assimilation could be 35, 50, or 70% for all we know .... Well that individual is a crank of the highest order with absolutely no respect for evidence or the principle of material conservation. The method makes a practical estimate that would be useful for anyone budgeting/tracking nutrients.
In the application of scientific principles, we often take metrics that are established from prior conducted experiments and apply theoretical models to solve practical problems. The reason this is acceptable ... is because we don't know of evidence falsifying the theory but have found evidence to be consistent with it with acceptable uncertainty. Where it comes to nutrient budgets, these have been practiced in planted crops for a long time where the objective is to maintain soil fertility and crop production. But the crop is the primary production and that is all we are trying to grow. Its an annual thing. A pond hosting an biome year after year serving as sink of nutrients is much more complex and in most cases doesn't need nutrient addition to replace what is harvested. Particularly Nitrogen, which in most areas of the eastern US deposits at 10 to 15 lbs per acre per year just from precipitation. This is enough nitrogen to supply the nitrogen proportion of 312 lbs of BG. This contribution is small relative to nitrogen that is fixed by bacteria and so we don't need any help from feed when it comes to nutrient accumulation, it will happen anyway.
Also BTW, there is evidence that addition of carbon reduces ammonia and improves FCR ... this is documented. You should read up on it.
