I’m just getting a 5 gallon planted tank started. I did a fishless cycle. Once I added fish they all did well for a while and then all slowly started dying one by one. My water parameters were all fine and the fish had no visible signs of traum, except some of them had reddish gills. I have not added more fish because I want to figure out my problem first. Here’s my question. I noticed that a couple small pieces of rockwool had somehow been dislodged from one of the plants. Could this have been what killed of my fish? I imagine that rockwool would at the very least irritate the gills.