Sand turning orange colored when lights on

[cbs49er]

So my tank is about 10 months old, 20 gallon with weekly 5 gallon water changes. Lately I noticed my a section of my sand bed turning orange color when the lights come on. If I look very closely I can see very small brown grass like strands coming out which I’m guessing is aptasia? Anybody know what’s going on and how to treat?

 

[lapin]

Diatoms Vs Dinoflagellates (Reef Tank) Identification and Treatment | Reef Tank Resource

A common problem in aquarist's reef aquariums is the presence of brownish algae coating everything from the sand to the live rock to the glass. It can look

reeftankresource.com