All of the sudden alll of the koi in my pond are sitting on the bottom. Very much like they do in winter. 2 of my fish last week developed small red dots (about the size of a pencil eraser. so i salted and added fluke tabs; i also began feeding medikoi to all of them. Did a 20% water change after 48 hrs (last monday) and did another water change yesterday afternoon (no more salt added during the water changes). I checked water parameters and they look good. Am-0, Nit-0, pH-6.5; temp-80 deg F, pond is ~1,000 gallons, 40 gallon biofilter, and i have 10 fish, ranging from 6" to about 15". why are they acting this way? Any insight would be appreciated