I have an overstocked, heavily fed, yet way overfiltered 240. Filtration is a 100 gal sump MB filter with 100 L of K1 and a Eheim 2262 with about 18 L of Seachem Matrix. I have a gravel substrate, about 3" deep and do weekly 1/3 to 1/2 water changes. I vacuum the gravel weekly as well, which is why this is puzzeling. Over pretty much the entire gravel bed I have a lot of gas bubbles that travel up the tube of my python. I hit the entire floor of the tank EVERY week. I thought that H2S was a sign of anaerobic activity but I don't see how that is likely with my filtration and maintenance. I have no fish health issues from it, as the gas mostly goes out with the waste water. Do you who know more than me think this is H2S or another gas? Has anyone else observed this? I have no fish in this tank that stir the substrate.
