Diatoms...problem just won't go away.

[marie]

Are you sure it is diatoms? Does it trap air bubbles and look a like brown snot? If it does then it might be dinoflagellates

Diatoms aren't usually a big problem in a reef tank there are so many critters that eat it, the problem doesn't last long. Dinoflagellates on the other hand are a big pain and can be challenging to get rid of