What should I feed my fish?

I have 3 tanks. The first tank has goldfish and a African Clawed Frog, I feed them Tetramin Goldfish Flakes, and just had to feed them some pea innards because one started floating. The second tank is all Guppies, I give them tropical fish flakes. The third tank, my largest has sword tails, plat ties, black mollies, and ghost shrimp. I feed them My sis Shrimp and Tropical fish Flakes, alternating. I noticed their excrement has been hanging and it seems to be bothering the small platty. Any help is greatly appreciated.