Of course flakes are fine for saltwater aquariums with many made specifically for it. For the longest time all I fed was Prime Reef, Spirulina flakes, New Spectrum 1mm pellets (auto feeder also for away times), nori and I had a tank full of fat happy fish. Being I have switched games with more soft and LPS corals along with a few new fish including nitpicky Anthias I have also gone back to feeding frozen mysis, brine, arctic pods, calanus along with oyster feast and occasional reefroids. The bad thing about frozen is spotty availability except online. I just dropped $136 + $30 shipping from BRS. Even at that they only had one Hikari frozen mysis in stock. Well price too... some of the boutique stuff out there is more expensive than premium human seafood.