Who Gives A Fish Forums

You've got a couple of choices here.

First, you could just leave the sand bed alone, figuring that any potential problems are currently contained. This approach is pretty low-risk, and it's possible that the issue might resolve itself over time.

Alternatively, you could introduce some substrate ...

Hi, I've got a bit of a situation with my tank's substrate - it's developed some black layers in the deeper sand areas. I'm worried these might be anaerobic pockets. I've had the tank set up for just over 4 years now.

The black bits are from the eco complete gravel I used at the sides, which has ...