Possible hydrogen sulfide buildup in substrate

[Kleger86]

I have a newly set up dirted tank that has been cycling (liquid ammonia, no fish) for almost 2 weeks. There is an inch to 1.5 inches of dirt with equal amounts of gravel on top. The dirt is specifically for aquariums. I also have a HOB filter and a sponge filter running. There are plants, some wood, and rocks as well. I’ve been doing 20-25% water changes every few days to get rid of excessive tannins in the water and I’ve noticed the water smells weird. When I went to do a light gravel vac to get rid of some of the built up diatoms a ton of bubbles were released and it smelled like eggs. I got my planting tweezers and started poking around and the tank erupted with bubbles everywhere I poked. After some research it looks like it’s hydrogen sulfide gas but I still have questions. How is it building up so fast, will it eventually stop building up, should I be doing something differently, is it toxic to fish and plants and the bacteria? If I skip a few days of poking around it’s like I haven’t done it at all there’s so much built up. Is it better to leave it alone? I’d really appreciate any insight! 

[Tony s]

I’ll help you get the ball going here. Other people will know more.

it sounds like your substrate is actively producing the sulfide. It’s probably just getting used to the aquarium. Probably not a problem if it was at the surface. But being capped, it can’t release the gas slowly. Yeah, hydrogen sulfide has the potential to crash the whole tank. And the ph spike it causes can kill your fish. I think you’re probably doing the right thing by stirring it and releasing it. Hopefully this settles down over a couple of days or weeks.

[doktor zhivago]

It's an anaerobic process in your dirt where bacteria break down sulfates into sulfides. It's building up so fast because there are a huge amount of sulfates in the product you used. Honestly no idea what the solution would be other than to let them pig out for a while

[Kleger86]

Thank you! I’m not in a rush to add fish to this tank so I’ll just try and wait it out and keep poking at it. 

[Tanked]

Hydrogen Sulfide accumulates in deep substrate and under hardscape, the anaerobic areas the others already mentioned. It is lethal to fish in concentration.  I have read where bottom dwellers will be the first to go due to the higher concentration.  Additional surface movement, aeration, and proper substrate cleaning can help.  I believe it will subside as the cycle completes.

[johnnyxxl]

On 3/5/2024 at 8:01 PM, Kleger86 said:

I have a newly set up dirted tank that has been cycling (liquid ammonia, no fish) for almost 2 weeks. There is an inch to 1.5 inches of dirt with equal amounts of gravel on top. The dirt is specifically for aquariums. I also have a HOB filter and a sponge filter running. There are plants, some wood, and rocks as well. I’ve been doing 20-25% water changes every few days to get rid of excessive tannins in the water and I’ve noticed the water smells weird. When I went to do a light gravel vac to get rid of some of the built up diatoms a ton of bubbles were released and it smelled like eggs. I got my planting tweezers and started poking around and the tank erupted with bubbles everywhere I poked. After some research it looks like it’s hydrogen sulfide gas but I still have questions. How is it building up so fast, will it eventually stop building up, should I be doing something differently, is it toxic to fish and plants and the bacteria? If I skip a few days of poking around it’s like I haven’t done it at all there’s so much built up. Is it better to leave it alone? I’d really appreciate any insight! 

I think this is why MD fishtank puts bags of old substrate under his soil before he caps the sand