I had the diatoms pretty bad too they would grow and then i would blast them off with a pipet and 3 hrs later after gettin back from class there it would be again mocking me LOL. get a fighting conch. Ever since adding mine I havent had any brown diatoms on the substrate....however it has all moved to my frag rack and the upper rocks where he doesnt go. So now im running seachem phosgaurd and more aggressive skimming and its fading away on my rock work and frag rack.