brown/bronze color snad

[bjohnston]

I have a 210 gal reef tank that is a year old with a 3 to 4 inch sand bed.
Everything seems healthy - rock - coal - fish - inverts however my sand bed has developed a brown/bronze top layer covering about 30% of the sand surface.

Is this something I need to be concerned about?
Should I try to remove it?

 

[afishyonados]

When did you change out your lights?

 

[bjohnston]

I changed my actinic bulbs last month. I have not changed my MH bulbs yet.

 

[melosu58]

I have two sand sifting gobies that turn mine all the time and it turns back to white.

 

[afishyonados]

Can you increase the water flow in the affected area?