fish food companies make sinking food such as shrimp pellets, etc. for the bottom feeders. some flakes may also fall to the bottom, and will be found by your bottom dwellers. If u can't get sinking foods for 1 reason or another, release some flakes underwater and they will fall for the bottom feeders.
I would only feed twice daily. I usally only feed once daily, but that's because my fish are getting too fat.