Brown Scum in Tank
Good morning, I am posting here because I am not an expert when it comes to fish, still kind of a begginer, but I was hoping to get some help.
We have a 20 gallon Freshwater Tank, we have 4 black tetra, 2 red barbs, 2 Dyno, a catfish, and a Plecostomas (I'm probably spelling that wrong). We have aplastic log, a fake plane, and a bunch of plastic plants, all from Petsmart and started the tank last July.
In our old apartment, we had city watrer, and we had to use the dechlorinator, just in case, but now we run on well water, and the well water does have a bit of sulfur in it. We've been in this apartment since November, and in March I noticed that the rocks were turning an orange color (like rust) And the fabric plants I had in there were stained black. So I got rid of them and replaced them with plastic plants, did my normal cleaning of the tank, put in the Water Conditioner for heavy metals, and thought I got rid of the source of the scum. A month later, we cleaned it again, and I scrubed all the new plants with hot water to get rid of what was on them.
Now it's been a month and all the plants are coated in a brownish/blackish scum and even though we've cleaned the tank twice, and gotten new plants, it feels like it's getting worse. 2 fish have dies n that time period, a Sword Tail and a guppy that we've had since the beginning, and another cat fish. I don't know if they are related or not. My mother in law's catfish keeps having babies, and we were going to get 2 more, but I don't want to put them in the tank if they might die. Any thoughts would be appreciated. I hope I put in enough information.