It's only on the bottom layer of sand in certain areas. Problem really is I used various different sands including fine grain and pool sand (silica). Both can cause my problem but I didn't think anything of it because I have great flow
Haha I'm not an expert but definitely not a noobie. It's anaerobic. Without a doubt, smells like sulfur, bottom layer of sand, the actual sand grains are BLACK. My options are to go with no sand or double or triple my sand bed depth. Otherwise it will be a constant bbattle.