It started with a single species. I used to keep Glofish (GM zebra danios). Lots of them, since they successfully spawned. Kept them for months without issue. Never had a single death for them, or any other fish, as a result of a water change in many years of fishkeeping.
Then all of a sudden 50% water changes started killing them. Most times, it would be one or two. But sometimes, every last one would be drop dead within two minutes. Other fish seemed unaffected.
Adjusting pH and temperature of tapwater didn't help at all, nor did extra Prime, or heavy aeration with an airstone. Reducing water changes to 33% solved it for the most part. But here and there, seemingly with the frequency that I formerly had mass deaths with 50% changes, I'd lose one or two. And if I got distracted and accidentally drained and refilled even 40%, the chance of deaths shot up.
Eventually I lost them all. I went back to 50% water changes, as 33% really didn't remove excesses from standard EI adequately.
Things were fine for a few months, until one day after a water change, multiple fish looked stressed or were acting strangely, and a couple died. Both were guppies from the same spawn. Thought it might have been a fluke, or a mistake on my part, so I started paying particular attention during water changes. A few months later, it happened again. Lost some guppies, cories were stunned and laying motionless on their backs. And this time I was sure there were no mistake, or anything odd about the replacement water that I could find.
What I do now is this. Drain 50%, add Prime, fill 25%. Move on to the next tank. After all tanks are done, go back and finish filling the tanks. Seems important that at least 15 minutes must pass before finishing the fill.
It works. Been more than a year and no problems. I'm just not sure WHY it works. Filters are running and churning bubbles into the water during this time, so maybe it's a gas content problem; but running heavy airstone aeration didn't have the same effect, at least for the Glofish. Or maybe there's more chlorine than normal, and Prime doesn't work fast enough to keep a full refill within safe limits.
I get city water quality reports yearly, they were using chloramines long before the first problem occurred, and nothing else in the report has substantially changed either.
I posted this on TPT a while back. As well as did an extensive web search for anyone else who might have had this problem. I did find reports from two people who had the same problem with regular zebra danios, but no solution was found. You're the first to report anything like I've seen.Statistics: Posted by Darkcobra — Mon Mar 11, 2013 7:00 pm
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