Pictured below is a visitor feeding my fish Nori Seaweed. Note: The Desjardini Sailfin Tang pictured below I personally owned 18 years until she outgrew my largest tank & I donated her to the New England Aquarium in Boston, MA on 1/27/2016 where she enjoys a BIG house (5200 gal Indo Pacific tank). Proof you can trust what I'm about to tell you below...
What to feed your fish depends on what you choose to keep for fish. Most of us have fish that are primarily herbivores. I call them "Ocean Cows". :c) The foods I use & sell will satisfy the needs of plankton & specialty eaters as well. These foods have kept my fish not only alive but vibrant & healthy - some over 20 years! Just like land "cows" they love their vegetation so do not need their foods mixed up or changed frequently! They aren't like us who would tire of the same ole foods. They are like cows - never getting tired of their favorite food. Trust the below is all you need to keep them healthy ... and happy.
To Prepare the "Soup" Foods:
I like to use 2 bathroom size Dixie cups. Use one to thaw frozen PE Mysis shrimp & one to unthaw Calanus (fed once or twice a week), each in cold freshwater (from the tap is fine). Only thaw enough Mysis shrimp to provide about 4 shrimp per larger fish like Tangs and 1 - 2 for smaller fish like Clowns or Gobies.. Pour/strain the thawed Mysis shrimp through a net, rinse with fresh cold water then backwash net into a little cup of more cold water. This removes the unwanted packing juices that ends up being just food for nuisance algae. Pour your thawed Calanus (no rinsing) into the Mysis container then add your ON Formulas 2 flake food to the mix. I turn off my powerheads then use a turkey baster to suck up the soup & broadcast feed. I do not target feed & I do not recommend it either.
How Much & How Often To Feed:
Make & feed only as much food as can be consumed in a minute or two (remember ... most fish bellies are only as big as their eyeballs!!) & feed only once a day.
Feeding Tangs & Herbivores:
You’ll also want to offer a bit of Nori seaweed once a day too. Best to feed this first thing in the morning so they can graze on it all day & stay out of trouble. :c) Feed only as much as can be consumed by evening. Remove any not eaten and reduce the amount fed if much is left on the rock. Notice in the picture here all the smaller fish getting their share of the tiny Nori pieces broken off by the bigger fish so even Clownfish, Anthias & more will benefit from it! Note the fat fish bellies but NO nuisance algae. Your fish & tank should look like mine when a proper feeding regimen is followed.
I only feed my captive bred seahorses once a day but do understand that I feed a frozen cube or block of PE Mysis shrimp rubber banded to a feeder - magnet mounted on the side of the tank glass. The Mysis slowly thaws, some float away allowing them to chase or they sit at the feeder & pick as they like = allows them to feed longer. I know most other places recommend feeding multiple times a day but we run the risk of polluting their water & creating an algae/poor water quality environment for them which is bad for them.
Feeding Anemones & LPS Corals:
Once a week is all they need. On the days they are fed I will add a bit more Mysis Shrimp. I will give a bit to the fish first then go to my anemone &/or corals. Remember! Corals gain 99% of their nutrition from photosynthesis so do not think they will starve to death if you don't direct feed them!
Never save unused soup food! Discard any not used, just prepare less the next feeding. Bacteria quickly grows in thawed shrimp etc. Always prepare new food for every feeding! Bacteria grows quickly on their food just like it does ours!
Again, you might want to consider turning off your powerheads/pumps during feeding so the food isn't blown into your rocks only to end up as excess nutrients! Having all your powerheads on a single power strip makes turning them off literally a single click on or off.
For information on what can happen if we over feed our tanks see Self Help Topic:
Feeding - Are You Killing Your Fish With Love?