Droppings will always reflect what is eaten. Gross as it sounds, a lot of dog owners can tell you something about their animal's health, just by their  bowser's feces. I'm sure agriculturalists can too, though this isn't a dinner time topic. Historically hunter/gatherers could use poison arrows, check the spore and figure their chances of dinner that evening.

Even fish heads can tell when a guppy has problems with something along the line of a Hexamida infection (white, stringy) or lonnnnng feces, indicating constipation. Scariest of all - no feces.

Fairfield even suggests netting the droppings of sick fish out immediately, putting them under a mircoscope and looking for eggs of parasites. This is beginning to resemble that list of the ten most undesirable science related jobs which was in the media a couple of weeks ago. (But Momma didn't raise me to be a lab tech.) ;)

At any rate, if you don't like the Tetra flakes, don't buy more. But I wouldn't just throw out them out. :)