Deciding when to feed your clownfish depends on the size of your fish. Adult anemones don't need to eat so much, so you can feed them twice daily. You can also feed them once, but that can slow down their growth. For younger clownfishes, you can feed them three to four times daily. Another thing is that you shouldn't put too much food in the aquarium at once. Only give them enough food that they can devour in three minutes or less. If you intend to feed them just once, then you can add enough for five minutes. Then, ensure you remove uneaten food quickly.