Tank smells powerfully of rotten eggs

[tentacles]

I don't think carbon will adsorb H2S under normal conditions; Wikipedia mentions using carbon as a substrate coated with a catalyst for reacting the H2S into less toxic/smelly compounds.

I think your best bet is probably some light peroxide dosing. And maybe check that biopellet reactor for cleanliness, if it's clogged and that smell is the bacteria dying off...

[Myka]

If there is a high oxygen level in the sump (such as after the skimmer) then the H2S will be at least partially oxidized where it can be removed by carbon. If there is H2S smell in the air carbon will remove it. GFO will also remove H2S.

[Myka]

There is this too... old, but still good info. http://reefkeeping.com/issues/2005-12/rhf/index.php

It mentions carbon and GFO, and gives you some steps to resolution.

[Dearth]

I deal with H2S a lot at my work although in considerably larger quantities than an aquarium tank will release and one of the easier ways to get rid of or diffuse the H2S is to have a continuous airflow with fresh air. All is required is a standard house fan and a source of fresh air IE. another room, fresh air from outside or just circulate throughout house. You can smell as little as 2 parts per million of H2S and while not generally harmful at those lvls prolonged exposure will give you symptoms but over a period of days anything over 10 parts is considered to be detrimental in as little as 8 hrs.

However that being said if you feel nauseous or have a headache from the H2S smell stop circulating the air immediately and go outside for fresh air and drink plenty of water till you no longer feel nauseous or headache has gone fresh air is the best and easiest way to diffuse H2S I don't think aquarium tanks will produce enough h2s to cause those issues but you never know.

[asylumdown]

So it looks like We've solved the problem, it was the drain trap in the emergency drain under the sump that had dried out.

With all the people that have been here, I didn't open the doors to the cabinet for several days, so the sewer gas was building up above the sump for who knows how long, and enough of it must have diffused in to the water to make the water smell. I siphoned some water in to it, and the smell in the house was gone in an hour. I switched my GFO reactor to a carbon reactor, did a 50 gallon water change, and the smell is now completely gone from the water. A couple corals have bleached a little, but things seem to be ok as far as I can tell. I'm going to need to remember to fill that drain on a regular basis.