dark brown algae.

Hello everyone. I am currently dealing with a problem with my 48 gallon tank. The tank has been cycled for about 3 months now. I have 3 clownfish, 1 anemone, 1 mushroom and 2 acros....Since last week, my tank has been filling up with brown algae and i cannot get it to stop overtaking the tank...

i've had this very dark brown algae (I'm assuming) for about 3 weeks. Water parameters are good. I've do water changes weekly, approx 20-30% and siphoned sand twice. No change. It's only on sand in front. I decreased amount of timeights were on but did not notice any difference. I appreciate...