agreed,the requirement perhaps cannot be accomplished for many marine species...however, in regards to some omni triggerfish species, it may be easier and more practical than many.
also..large pomacs that consume 95-99% sponge with the remainder algae may be an option as well. however,,some pomacs consume 20 different varieties of sponge so that may be a nonpractical challenge.. but unless you identify what the difference is b/t the varying sponge contents..how would you know those would be included in the commercially available additives?
ps...i'm not really at all disagreeing with anything in your overall post here... i rarely have found anything to contradict with regards to what you write..,if ever..
