Aquarium fish in the wild are lucky to eat once a week. They may eat well one day and then, not eat for a couple of weeks. These fish are built to go at least a couple of weeks without food. So, unless you have fry you're trying to raise, your fish don't need to eat but a couple of times a week. They'll forage around the tank for every leftover and your tank stays cleaner, longer.
The key to healthy fish is feed a little, but feed a variety of good food. Frozen is probably the most nutritious. It has the fewest additives. Additives simply extend the life of the product and aren't necessarily good for the fish. Look for frozen bloodworms, any of the shrimps like brine and Mysis, plankton, krill and beef heart are very good.
Minced garlic is a super food for fish. It has no additives and is loaded with vitamins and natural antibiotics. An algae biscuit is good once or twice a week.
In general, look at the contents on the label. If there's a name you don't recognize, I recommend passing on it.
"Fear not, my young apprentice. Just change the tank water."