Green and Black Color Under DSB

[67Stang]

Was just checking out my reef and noticed a green and black color just under the DSB.

It can be seen from the front of the tank through the glass. It's between the glass and the sand. It's been a slow process forming but now I'm wondering if this is a sign of trouble to come.

I looked under the tank and didn't notice it on the bottom.

Tha tank is 200gal reef with a 4"DSB. 2 Metal Halide pendants on 9 hours/day. Water quality is perfect. No excessive algae anywhere in the tank. All fish and inverts doing great.

What would you guys recommend?
Should I just leave it or take some kind of action?

Thanks

 

[Enkidu]

I think I've noticed a similar effect in my tank. What I noticed was pretty much black and blue, like a bruise in the sandbed. I noticed quite a bit of it when I was moving sand around and I picked some up and gave it the sniff test and it smelled pretty gross. I assume that its just bacteria doing its thing so I'm not too worried about it but then again my tank is only a couple months old so there could be a problem that hasn't made itself obvious yet.

 

[jmeader]

The green is most likely algae. It will grow anywhere it gets enough light and nutrients. The black is normal. Anaerobic areas generally turn black when they first form, but quite often change back again later.