I hung a 175 watt pendant metal halide light 10 inches over my tank. I'm using a coralife 175 watt, 20,000 k
bulb. To my suprise the light is slightly on the blue side. The tank became overrun with brown algae. Not even the turbo snails like it. I also did 2 large water changes to help get rid of medication right before hanging the light. WHAT IS THE PROBLEM? How do I fix it?
I'm using tap water. The water is a little hard (250), pH is 8.0 ( a little high), nitrite is zero, nitrate is 20 ppm
The algae is hard to describe. Its not filamentous or hairy and not in sheets. It is a thin, almost flat spotty layer that easily rubs off in extremely small pieces, almost like dust.
Before using the new lighting I used 2 Coralife 50/50 flourescent tube and got green and red algaes. Then 1 tube burned out and the brown algae took over. I cleaned the tank, scraped the algae, moved the tank downstairs, changed a lot of the water in the process, and switched to the Metal Halide pendant. The brown algae went nuts.