NANFA-L-- Killer Rain, Stratification, H2S

Gerald Pottern (gbpottern at
Thu, 8 Sep 2005 14:18:53 -0700 (PDT)

Todd & Nick -- Hmmm... well ... no i guess i cant unequivocally say i've seen an H2S effect. I've seen heavy breathing & erratic swimming sometimes when i stir up gray clouds and bubbles from dirty gravel, and assumed that H2S was a cause. One of our recent local club speakers, aquatic gardener Diana Walstad, said that H2S from anaerobic gravel can be a chronic stressor on fish and plants, so i figured a sudden pulse oughta be an acute stressor. BTW - Diana also thinks that having a little iron-rich clay in the gravel will precipitate the sulfur as iron sulfide and thus protect fish & plants from H2S damage. Any thoughts on this ???

(Diana -- this NANFA discussion came about from sudden die-offs of pond fish & algae following heavy summer rains. Theories so far include temp shock, pH shock, CO2, and de-stratification dynamics).

So, what IS in those sediment clouds & bubbles, and why do i see the apparent stress reactions when i stir up too much dirty gravel (especially in shiners) ? I dont think ammonia would accumulate in gravel/sediment - it's too soluble. Also hard for me to believe that simple physical irritation from the particulates would cause this. Could something in there be causing excessive mucus production on the gills and thus suffocating the fish ??? i sometimes see dirt sticking on their skin, which suggests a mucus gland reaction. --gerald

--------- Todd Crail wrote : Hi Gerald, While H2S is definately a caustic molecule as it acts like cyanide in the bloodstream, binding iron at certain levels that may seem low (in micrograms per Liter)... My understanding is that it takes such a concentration of H2S to reach the levels where LD50 tests have shown mortality in fathead minnows due specifically to H2S (like you would literally begin to barf as it evolved from the tank) that there would have been far more nefarious conditions in the aquarium (such as NH4+) before the H2S was in any part, the causative agent.

I can also anecdotally vouch for the presence of H2S in systems having no observable effect in my systems. With my deep sandbed approach, I am rotting material continually, to the point where moving rocks sends plumes of black nasties, and clear bubbles, without any problems. As I mentioned, I think people are having problems in their tanks because of other issues,
catch a whiff of something rancid, and assume that was the problem, while far more volatile and caustic chemicals are running around.

And theoretically, we also have to remember that each night in these systems, the thermocline would break up, and the system would slowly mix back together. This would dissipate any H2S trapped in the dissimilar chemistries as you had mentioned, and avoid a situation where accumulations could become deadly... Such as the mixing event in Cameroon a few years back, where a deep, stratified volcanic lake mixed and effectively gased everything within a certain radius... Much like Dad after Thanksgiving dinner :) Actually, I shouldn't joke, because it was quite devestating... But I couldn't resist the analogy. Todd The Madness (tm)

---------- Nick Zarlinga wrote:
Date: Tue, 6 Sep 2005 20:47:01 -0400
From: "njz" <njz at>
Subject: Re: NANFA-L-- Killer Rain, Stratification + H2S

Good job Todd!
As far as Hsulfide, I have never seen an effect on fish. It always amazed
me since I have smelled some pretty rotten stuff. I do beleive that even a
very small concentration is very potent to the olefactory senses. You have
definitely seen an effect on fish attributed to this? Nick Zarlinga

Date: Tue, 6 Sep 2005 13:03:42 -0700 (PDT)
From: Gerald Pottern <gbpottern at>
Subject: NANFA-L-- Killer Rain, Stratification + H2S

Todd/Geoff/Nick/Moon/Mystery & killer rain sleuths - even if the
hypolimnion (cooler bottom water) of the pond wasnt anaerobic yet, there
could have been a lot of hydrogen sulfide H2S down in the detritus layer,
that got churned up by a rain-induced turn-over. You can watch fish
stress out even in a well aerated aquarium if you stir up deep dirty
gravel full of aged fish poop (and smell that H2S). Its very toxic stuff,
but oxidizes or dissipates ??? pretty quick after mixing in aerated
water. gerald -- hangin on the neuse, NC

Click here to donate to the Hurricane Katrina relief effort.
/ This is the discussion list of the North American Native Fishes
/ Association (NANFA). Comments made on this list do not necessarily
/ reflect the beliefs or goals of NANFA. For more information about NANFA,
/ visit Please make sure all posts to nanfa-l are
/ consistent with the guidelines as per
/ To subscribe, unsubscribe, or get
/ help, visit the NANFA email list home page and archive at