scarab

Oh! so I should just not on lights at all???

Hi! I'm cycling my tank for about a week and discover some brown algae-like thing growing on my live rock. It doesn't grow on every rock just some. Some even have no sign of it. Some hair like thing seem to be growing from it. Anyway my tank is 42 by 24 by 24 in which work out to about 100 gallon (I think). I started with DI water. Salinity last checked was 1.023. Using 2nos 150W metal halide c/w blue actinic switch on for about 8 to 10 hours daily. Live rock was precured at farm for 2 weeks before introduction. Total live rock weight about 55 kg. Water test show low ammonia(<0.5mg/L) and nitrite (0.2mg/L). Haven't tested for nitrate yet. What are these and will it bloom in the tank? Thanks. sorry one more thing. have been seeing air bubbles escaping from my sand bed during this period. is it normal?