I am new to the forums, and would still call myself a newbie at aquariums.
I have had a 29 gallon freshwater tank for about 5 years. Where I live before I had no major algae issues. The tank got green algae but it was just a minor cleaning nuisance.
I moved in July. I brought along the same gravel (well cleaned) and my live plants. The fish I didn't, I took them to a local pet shop rather than kill them. Two days after moving I set my tank back up, using the gravel and the plants from before. I let it cycle for 2 weeks, tested, everything was acceptable. Went and bought 3 black skirt tetras as my testers. Two weeks later they were fine, so I added 2 cory catfish, 1 rubbernose pleco, and 3 more tetras. Two or 3 weeks after that I did my first cleaning. It wasn't very dirty, didn't do more than 15-20% water change.
I had issues getting correct water temperature to replace the water. For some reason cold water was more warm than cold, so the replacement water was a couple of degrees warmer than I liked. Within 2 days one of my cory cats died. I figured it was due to the water temperature. Faster forward to next cleaning, same issue with water temperature, but don't think that was an issue. One day after that cleaning I notice white stuff on the gravel. It spread pretty quick and next thing I know my other cory and pleco are dead. The tetras were just fine. I clean the tank and had to agitate the gravel just to get the stuff off.
Needless to say, it came back. I pulled the gravel out, cleaned it by hand, cleaned the filter, and everything else. I replaced as little of the water as possible since knew was risking a lot with that much cleaning. The tetras were troopers tho and made it thru it all. It looked good, didn't see any signs of any growth coming back, so I added 2 cory cats again, as I needed bottom feeders to clean. Week after, I did a small cleaning again. And the next day or so the stuff showed up in the gravel again. I've tried fungus treatment. No luck. I could replace the gravel, but I'd prefer to find the solution before replace stuff just to have it return. Anyone have any ideas for this?