White sand turning black?

[Justin0329]

I have white Fiji sand in my 55. Its really fine grain. Tonight while doing a pwc and vacuuming the sand bed, I noticed the sand below is turning dark. Almost black. My guess is that its not good. I stirred/turned the sand bed really well and did a large water change. About 50 to 60 percent. Any ideas what is causing this or if it is in deed a bad thing?

 

[boardsurfer]

Can you post a picture?

 

[Megatron]

What are your tank parameters?

 

[boardsurfer]

Btw, I wouldn't suggest turning up the sand. I would siphon it up with you pwc.

 

[Rutrag]

The sand below the surface is likely anoxic and will normally be darker. Stirring it may release some nasty stuff and actually might make you lose some beneficial bacteria that likes that kind of environment.