The tank is dirted, and has had fish in it for around 6 mo. Plants were in the tank alone for several months before that. The tank had 5 cory cats and three celestial pearl danios. 1 cpd must have died 1-2 weeks ago. I did not find the body. 1 cory cat started swimming erratically and basically appeared to lose consciousness mid water and fall to the tank floor. By the time I got it out of the main tank to put into the hospital tank it was already dead. These are fish ( 3 cory sp) that were moved from my 55G to the 30 gallon after they were seen having similar symptoms in the 55G. Yesterday one of my Cory punctatus was laying on some moss appearing unconscious, I put it in the hospital tank and it died several hours later.
The nitrates are 5ppm, the nitrites were 0ppm, the ammonia appears more 0.25ppm than the yellow of 0ppm although it does not look as green as the 0.25ppm color block. pH was 7. GH as measured by api stick was 180ppm ( I have measured the api sticks to the liquid tests and the hardness and pH are true).
The remaining fish have increased redness around the gills.
After the 1st death when I did the 3 -10% water changes I did use a water conditioner and the water sat overnight as well. One thing I noticed when I was filling my water buckets was that my sink spluttered. The 1st water change I was using luke warm water by mixing hot and cold. Earlier that day when I was filling my dogs water bowl and I first turned the hot water on that day I thought the hot water was cloudy, possibly a small amount of rust. By the time I was doing the 10% water changes the water was running clear. But from then on I only used the cold water, which was why I let the water sit overnight in the room with the fish tanks, so that the water could warm to room temp around 70-72F.