The hardest thing for me to do has been to learn to feed them less.
It's strange to me how often I hear warnings about overfeeding. I generally feed my fish 3 times a day, pellets not flakes. The latter do foul the water far more than pellets.
My discus pair are nearly insatiable, as are my blue neons. My Bettas eat until their satisfied, which is fairly quickly. Whatever is left, which is very little, gets cleaned up by my L134. I actually worry about the L134 not getting enough, so I drop in an algae wafer every now and then.
I have never had an issue with "foul water". It's certainly not impossible to overfeed, but it seems to me you really have to go overboard.
As for the OP's question about food type, fish can be picky. I've tried most of the major brands out there and my fish seem to prefer Tetra Bits Complete, Hikari Vibra Bites, and a Tetra Bits knock-off that's locally produced (and cheaper). They have not taken to any other Hikari product, most other Tetra products, Ocean Nutrition, NLS, or Bug Bites. Though as stated, I stay away from flake food. My fish have even been picky about some brands of freeze-dried worms.
Experiment until you find what they like, as long as it's a balanced food. Live and frozen foods lack many essential nutrients, so those should not be relied on.