Dirty Tank Scare


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1 year
tonight I was adjusting a dwarf chain sword. It has a runner with 3 clumps of leaves, with roots under each clump. So proud of how the plants are doing in this tank.

This morning I noticed the runner’s roots were no longer in the substrate, figured a Cory had gotten under it and pulled the roots out. As I was replanting the roots of all three clumps, I pressed down on the substrate. Boom, large bubbles emerged. I touched about 2” away more bubbles. I ended up pressing the entire bottom and got 15-20 bubbles, some large.

I’ve read about anaerobic events with some type of sulfur gas getting caught beneath the substrate and when it releases, it kills the fish. I did smell a little sulfur type smell, kinda like Prime but less so.

So it’s 2 hours later and lights out but the fish look normal.

My initial thought was to move them to a couple of tanks that have room.

Am I past the scare?

Guaranteed i’ll Be pressing the substrate on that tank regularly.

Edit: the substrate is organic potting mix capped with BDBS. And the tank is only about 5 weeks old.


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More than 10 years
Perhaps check mid-week at a depth of about 1 inch, (lightly agitate and probe the substrate) as IF it's hydrogen sulfide gas, it could mean you may have to lighten burden of oxygen, and also the capping on your dirt, as "normal" blasting abrasive's typically used in sandblasting on houses, but over time with weather factors considered, I.E. water, it's primary molecules will shrink, thus "tightening" any molecular space in-between and in effect, making any substance's clearance restricted then longer it's threshold's maintained. And yes IF it is hydrogen sulfide gas, your fish will likely die within only a couple of hours IF it were. Hopefully not!

Wait...it's ONLY 5 weeks old? It could be just root tabs or something's chemical micro and macro stuff etc. getting caught up in air bubbles is all since it's not a super, potent smell from the bubbles. Especially if you say that the fish are fine. : )


Well Known
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East TN, USA
5 years
I suspect it might just be something harmless going on with your soil under the sand. From what I understand, no gas will linger in your water column for long, especially if it's moving water with good surface agitation. I think the main danger of hydrogen sulfide (kinda the worst case scenario for what those bubble were) is that it's heavier than oxygen, so it can gather just above the water and cut off the water's access to oxygen in the gas exchange, which can cause your livestock to suffocate. If you don't smell it there, it's gone. If you do, move a fan over it for a minute and it should clear it away. An Airstone might help too if you don't already have one running.

If I'm wrong here, please someone correct me. I've never experienced it first hand, but I have tanks with deepish sand in them for plants so I read up on it a while back. I hear a lot of people warning about the possibility of anaerobic bacteria creating hydrogen sulfide, but not a lot of people who've lost fish to it.

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