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Re: H2S Good or Bad?

From: larry at creative_net (Larry Frank) 
>> I set up a new tank about 10 days ago. For the substrate I used
dirt ( red stuff from Sedona AZ. I figured it probably contained a lot of Iron?)
mixed with #3 and course aquarium gravel, in a ratio of about 1 part dirt to 8 
parts gravel. The tank is 185 gallons, and the substrate is 4 to 6.5 inches 
deep. 2/3 gravel  mixed with dirt, and the top 2 inches washed gravel. I have a 
250 watt dupla cable which is on all the time, keeping the tank at about 82 
degrees. I initially planted the tank pretty densely, with mostly bunch plants 
and swords. Today I noticed random bubbles escaping from the gravel. When I
disturbed the substrate more bubbles escaped; the odor smelled a little 
sulfurish. I figure I probably have anaerobic areas and, I am producing 
H2s? <<

These bubbles are primarily methane, CH4. The smell is primarily 
methyl-mercator, HS-CH3 which you can smell at extremely low 

>> Is this REALLY BAD? DO I need to start over again, before my
investment in plants disappears, - using something safer like laterite? <<

In my opinion, it's not a reason to panic. Such chemicals occur in many natural 
waters in low concentrations. The volatile and very toxic ones like H2S are very
rapidly oxidized near the surface of the substrate (1-2") so long as there is 
oxygen dissolved in your water (which there must be else the fish would expire) 
If you collected your dirt from outside and it has little or no plant matter 
visible, chances are this activity is going to decrease in a few months. It will
probably increase for the short term.

>> Or perhaps this is a good thing that will reduce the nitrates? <<

This won't reduce nitrates. If the soil was fertile and contained 
organic materials, it may increase them. Since discus are normally fed 
well, you'll probably be getting plenty of nitrogen from the fish food 

>>Is this condition dangerous to the fish. So far the four small
discus in the tank look happy! <<

I don't know much about discus keeping and these fish tend to be expensive. 
If I were you I'd read up on discus and do some water testing especially 
for ammonia, nitrates and hardness. Does anyone know if discus are kept in 
humic water? I usually like to keep a tank with a new substrate without 
fish for a few days until I see where things are going and then add the 
catfish and one or two platys. Since I'm using peat in the substrate in my 
latest tank, the fish will be mostly catfish and tetras. About the only 
plant which might be sensitive to water conditions that I know of is the 
Madagascar lace plant. Some plants are growth inhibited in very fertile 
substrates but some thrive under these conditions. Your substrate is not in 
this category so I wouldn't worry about the plants. Perhaps Paul Krombholz 
will comment since I think he is internet connected once again after a 
brief interruption. My feeling is that the more organic material is in a 
substrate, the more plants, light and nutrients you should have to ensure 
that the oxygen concentration remains fairly high. Stable humic compounds 
such as phenolic compounds (ie blackwater extract or peat water) which give 
a yellowish tint to water are something which some fish need and others may 
not. If your fish prefer oligotrophic waters with few nutrients and DOC, it 
is always a good precaution to use regular activated carbon filtration. I'm 
not sure which category discus are in other than they prefer soft water. 

What is the annual rainfall in Sedona AZ, Larry? Desert soils may be 
alkaline and should be avoided. I would try to choose soil from a hill or 
well drained location preferably one from an area which received more 
rainfall i.e. the windward side of mountains if it was an arid region. If 
the soil was suitable for growing a variety of plants it should be ok. You 
can always test the pH and hardness factors.

Steve in Vancouver BC