Need Advice after Multiple Deaths in 48 Hour Period

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??
 
Your welcome

Just make sure to use the aap Medicated wonder shell, not the weco, these will not help for this problem
 
Sounds to me like it could be columnaris, like Gregg said. There seems to be 2 forms, 1 is fast moving, the other more chronic & slow. But it may also be more than 1 issue (ich spots?). I have heard of wonder shells but never tried them. Does it kill off the beneficial bacteria?

Adding new fish to either a "sanitized" tank or treated tank is a risk each time.
 
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