Hi, I am new to this site and am looking for a little help. I own a 300L reef tank which has been up and running for 4 years now. A few months ago I started to get a brown algae covering my sand, live rock and corals. This wipes off really easily but is back 10 minutes later. When I brush it off the rock etc it seems to have lots of tiny little air bubbles in it. It is driving me mad I have tried everything I can think of. I use rowaphos and my phosphate reading is 0 and all other water parameters seem fine. Ammonia 0 Nitrite 0 Nitrate 5 Calcium 450 Ph 8.1 KH 10.2 Temp 76 Salinity 1.023. My tank runs on live rock and a deltec skimmer that i clean out weekly. I have 2 250w halides and 2 T5 blue acnitics which I have also changed but this has made no difference. I have siphoned it out used the net but it always seems to come back. I have also done large water changes but still no difference. If anyone has any idea what this is and how to get rid of it i would be grateful! Thanks Amelia