Pond Hydrogen Sulfide

Hydrogen Sulfide gas is a gas produced in an-aerobic pockets under pond water. These may occur anywhere there is deep sand or sediment, or in a sump with thick mulm. The key elements in Hydrogen Sulfide elaboration by hazardous anaerobic bacteria are still water, deprivation of oxygen in deep media, and time. Lots of time.

Koi ponds with more than a few inches of gravel on the bottom will develop noxious gases including methane, Hydrogen sulfide and toxic levels of Carbon Dioxide.

Without Oxygen, some bacteria can respire by using Sulfur, and this creates Hydrogen Sulfide, H2S that is very, very toxic to fish. HACH Chemical has a test for this, (1-800-227-4224) but this should be suspected in any case of koi fish loss where:

1) There are no koi or pond fish parasites, proven by microscopy,

2) There are no real Ammonia or Nitrite derangements

3) The signs are respiratory, the koi fish are gasping at the surface

4) The history has some reference to a stalled filter or the stirring of deep, stagnant gravel or media.

The smell is one of rotting eggs. Losses may be great and they will continue after the H2S is long gone.