Currently have a 20 gallon IM all in one tank. It's been running for over a year and previously converted from a 10 gallon. When I converted I transferred rock with brown brush algae to the new tank. I tried to brush it off to no avail and the algae persisted in the new tank. Recently I've decided to turn off the brighter daylight bulbs and kept the blue bulbs lit. The tank has mechanical filtration with Chemi-Pure Blue, a small skimmer and a media reactor with Phosphate Out. The brush algae seems to be morphing into a slime like substance that coats the rock, glass and substrate. I try to remove as much as I can periodically with a toothbrush. It comes off in sheets but it persists. Does anyone know what this stuff is?