Are you sure nothing else changed? Seems very strange to have any infection take down so many fish so quickly. I could see if it happened over a week or two, but not hours.
Did you do anything different recently? Many years ago I cleaned the glass of my tank with a new sponge. Didn't realize it was a sponge that was toxic to a fish tank. About five 90% water changes in a row saved most of them. I'm just thinking maybe you had some kind of an "event" which led to the deaths??
Did you do anything different recently? Many years ago I cleaned the glass of my tank with a new sponge. Didn't realize it was a sponge that was toxic to a fish tank. About five 90% water changes in a row saved most of them. I'm just thinking maybe you had some kind of an "event" which led to the deaths??