Originally Posted by Thomas712
This is fairly normal for any sand bed that is above the plastic line, or even below for that matter.
It could be:
1. The bacteria that you speak of that helps to process nitrates, these usually show up as dark ~ even black colonies of bacteria. These are areas of low or no oxygen known as anoxic regions.
2. Since it is an exposed area to light then you could very well have algae colonies as well, this too is normal. These can start out green or even red, and sometimes wind up very dark as they eventually get starved out.
This is one reason a good cleanup crew will have nassarious snails, chitons, or even a fighting conch, as well as a healthy population of pods and worms.
Thomas
It's algae like you said. I have clean up crews, I couldn't clean that part off cause my magnet scrubber couldn't do it, I'm gonna get a scrub pad to do so. And yes I have anoxic bacteria in my sandbed plus worms etc. :happyfish