[APD] hydrogen sulfide - help!

[Mark Gilmore <gilmore at ece_unm.edu>]

Hi All,

I've just had the worst disaster of my fishkeeping career and I need 
some help.

I have a 75 gal planted tank, that is 5 years old, and I thought was 
very healthy.  I clean it and change 10 gal of water every 1 - 2 weeks. 
  I vacuum over the surface of the gravel, but don't typically push the 
syphon into the gravel, so as to not disturb plant roots.

Yesterday I cleaned the tank, and I removed a large piece of driftwood 
to clean algea off of it (which I did with a scrub pad).  Also I 
uprooted a stand of Bacopa, chopped it and replanted the tops.

I restarted the canister filter, and within about 2 minutes fish started 
gasping at the surface.  I couldn't figure out what was up.  I shut off 
the filter, and CO2 injection.  When I lifted the lid I smelled sulfur 
strongly.

I squirted in Amquel and set up a 10 gal tank as fast as I could to 
remove fish to, but too late.  Within 5 min, about 1/2 my fish died - 
about 20 of them.  This includes 3 siamese algea eaters that were over 8 
years old.  I'm devastated.

I'm guessing I stirred up a pocket of hydrogen sulfide, which poisoned 
the fish.  Maybe it was under the driftwood (???)  The filter must have 
sucked it up and dispersed it.  (I opened the filter before restarting 
it, but didn't smell sulphur).

Last night I changed 25 gal of water.  This morning, 2 fish I couldn't 
net were still alive in the 75 gal tank, and I couldn't smell sulfur. 
So I returned the survivors from the 10 gal tank.  So far they seem ok.

Has anyone had this kind of experience before?  Does my assumption of 
hydrogen sulfide release seem correct?  Can I assume the hydrogen 
sulfide released yesterday has dissipated?

I'm also worried about other pockets of hydrogen sulfide that may exist. 
  Does anyone have advice on how to safely deal with these?

My heart is heavy.

Thanks much.

- Mark Gilmore
Albuquerque, NM



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