Is anaerobic sand a concern for my aquarium?

[dash10]

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 mixed in a bit. I'm not sure if I should just leave it or try to address the issue. Any advice would be great, thanks!

[Avalon]

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-dwelling inverts, like Malaysian trumpet snails. These guys are great at burrowing into the substrate and cleaning up any debris. As long as you don't overfeed them, their population should remain under control.

If you're feeling more aggressive, you could always break down the tank and give the substrate a thorough cleaning. This would involve removing the fish, decor, and plants, and then either replacing the substrate entirely or doing a deep clean to get rid of any anaerobic pockets. You could also use this opportunity to reduce the depth of the substrate, or just leave it as is and add some snails to the mix.

[dash10]

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-dwelling inverts, like Malaysian trumpet snails. These guys are great at burrowing into the substrate and cleaning up any debris. As long as you don't overfeed them, their population should remain under control.

If you're feeling more aggressive, you could always break down the tank and give the substrate a thorough cleaning. This would involve removing the fish, decor, and plants, and then either replacing the substrate entirely or doing a deep clean to get rid of any anaerobic pockets. You could also use this opportunity to reduce the depth of the substrate, or just leave it as is and add some snails to the mix.

Thanks for the advice, it's really helpful. I'm keen to avoid breaking down the tank if I can. If I do add the trumpet snails, should I be worried about them stirring up the noxious gasses? I'll definitely leave the sand bed alone for now, just to be safe.

[boomer]

The black layer near the front glass is probably just algae rather than hydrogen sulfide. I'd strongly advise against disturbing the sand at all unless you've removed the fish first. Your substrate is pretty deep, and while some anaerobic patches are normal in a healthy setup, you don't want too many. The thing is, there's no real way to know what the whole substrate is like without taking a closer look.

[coltin]

I'm fairly certain it's anaerobic. To address this, you can try using a gravel cleaner to carefully release the trapped gases. By inserting the cleaner into the sand and holding it there for a few seconds, you'll allow any bubbles to form and rise up the syphon hose, rather than entering the water. Then, simply lift the cleaner and move to another area, repeating this process until you've completed a 50% water change. Follow up by topping up the tank with dechlorinated water. For future water changes, focus on another section of the substrate, gradually working your way through until the issue is resolved. One tip to avoid sucking up the sand is to slightly kink the syphon hose, which will slow the water flow.