Hi there, I picked up a few assorted platies a few weeks ago. Seemed fine (I even had a fry - that promptly got eaten I think), however, two died within the last couple of days and the remaining seem to have red gills. My other stock - some pygmy corys, beckford pencilfish, and amano shrimp all seem to be fine. Ammonia seems like its the main cause of red gills on the internet, however, I have 0 ppm ammonia according to my API test kit (see below). So I am wondering if this is a disease? Apologies for the quality of the images I will try to get clearer ones. Any help is greatly appreciated.
Water Parameters:
pH - 7.3-7.5
Nitrates - 40 ppm (moderately planted)
Hardness - ~8 degrees
Nitrite - 0 ppm
Ammonia - 0 ppm
KH/Buffer - ~5 degrees
Water Temperature - ~79 degrees