Hydrogen sulfate in aquariums...

[Molch]

everybody (incl. me) is afraid of the dreaded "black sludge" forming in the substrate and releasing highly toxic H2S.

however, in Diana Walstad's book "Ecology of the planted aquarium" it says (paraphrased here from p. 133):

all submerged soils are more or less anaerobic. High concentrations of H2S in the substrate can harm plant roots. However, as soon as H2S bubbles upward into the (aerobic) water column, it is immediately oxidized to harmless sulfates and is therefore no great concern to fish.

Yet, elsewhere in the book it states that fish can lose their appetite when H2S is present. So now I'm not sure what to think. Would H2S be present in that form or as sulfates in the water? And how much concern really are those sulfates?

So...what do we think about this? Just how dangerous IS H2S released from substrate for fish/newts?

 

[Opacum]

Would oxygenating the water, vis a vis an airstone, help? If oxygen converts the Hydrogen sulfide molecule (H2S) to Hydrogen sulfate (HSO4-) wouldn't dissolved oxygen via bubbles attenuate the effect? Even breaking the surface tension of the water with some type of overflow would help. Or perhaps an undergravel with powerheads with airstone attachments... Although then you might create too much of a current with those devices. You would have to deflect the turbulence with something. Just throwing this out there...

 

[Jennewt]

I was also a bit surprised that Walstad is tolerant of having an anaerobic layer, but it's true - in nature, the mud under the pond is anaerobic. My interpretation is that H2S is bad for fish, but as long as it's immediately oxidized as it emerges from the mud, no harm done. In other words, small amounts may be released, but they won't be an issue with the water chemistry as long as the tank water is aerobic.

 

[Molch]

of course, the plants' roots will also help oxygenate the substrate, as long as plants are doing well and cover much of the tank...that would keep H2S production down.

Still, if I remember my childhood newting days in good ol' Germany, many newt ponds had anaerobic soils with black sludge, and it didn't seem to hurt the newts much at all, judging from their thriving populations. It would come up in huge stinky clouds when the substarte was disturbed though, which why it was never a good idea to wade into a pond.......

 

[carsona246]

I've lost fish to hydrogen sulfide, but it was for an abnormal circumstance. I've seen tanks while researching freshwater dsb's that have huge black spots in their sand and their fish are just fine. I dont think theres too much of a risk of harming your fish with the dreaded black spots as long as you take care around them. Honestly though I wouldn't want any in my tank