Flakes-and granulated feed today are of very high quality and contain all the components, vitamins and fatty acids, which your fish need.
If you keep fish like surgeonfishes which feed on algae, choose granulate feed with a high green fodder and algae content or regularly provide Nori-algae.
On the contrary plankton feed or fluid feed are ideal for example for Anthias or angel fishes. Observe your fishes properly and feed them only as much as required for a short time. Also observe the effects of different feed- and quantities on the water values, especially phosphate and nitrate.