Hydrogen Sulfide

Hydrogen Sulphide is produced when there is insufficient nitrate but organic compounds are still available in an anoxic area of a DSB. This is one of the reasons that a fairly high flow is recommended over a DSB to ensure that enough nitrate is being produced to avoid the Hydrogen Sulphide reaction. In all DSBs a certain amount of hydrogen sulphide will be created. In most cases it is harmlessly filtered back up into the hypoxic and oxygen rich areas of the DSB and (as long as the flow is low enough) combines with iron and other atoms to reduce to various sulfphates which are non toxic. In very rare occasions you may have a situation where a pocket of hydrogen sulphide is produced and the sand bed is disturbed at that very same point. (Again, do not stir sand beds… this is one of the reasons why.) If this happens you will notice an increase in ammonium compounds (ending in a nitrate spike.) But, more worrying and more immediate you will smell rotten eggs as hydrogen sulphide is released into your aquarium. This is a highly poisonus gas that WILL KILL YOUR ANIMALS. You should immediately…

1. Turn off all flow to your main tank

2. Get a 50/50 Carbon and GFO media reactor going

3. Increase the flow to the affected areas as much as possible with as much surface agitation as you can get. Adding an airstone would not be a bad idea if you have one available

4. Perform immediate and large water changes, as large as you safely can and as quickly as you can

The event should be over in an hour or so as hydrogen sulphide is very unstable in saltwater which is why you are increasing current. It combines very readily to make Iron Sulphate which is why you are running the GFO. It also is adsorbed by activated carbon. Hopefully you cut off flow before it got too your main tank. If not you can treat the main tank separately as above. An excellent article on Hydrogen Sulphide in the aquarium is available at http://reefkeeping.com/issues/2005-12/rhf/index.php