by desrie.govender

Question by gvdvsq05: Help! After cleaning our pond yesterday, all our fish died! Does anyone know why?
We had four young koi (about five inches long), a lot of small guppy-like fish, four fish with long, fanlike tails (I forget the breed, they were about the same size as our koi), and three smallish algae suckers. The pond is definitely big enough for all of them.

The pond was very dirty (algae mostly). Our fish seemed fine though, no abnormal appearances or behaviours. The guppy-like fish were even breeding, so the water conditions were pretty good.

We cleaned the pond (keeping some of the old water so the new water wouldn’t be such a shock to the fish), and today all our fish are dead.

Their bellies are swollen (not as big as dropsy though), and the scales around their gills are red. Other than this discolouration, there is no disturbance in the scales (none sticking out or whatever).

My husband commented that the water smelled funny “sort of like dead fish”, but this was before the death of our fish.

Best answer:

Answer by Poopy
Sounds like chlorine poisoning – what kind of water did you use to refill the pond, and did you treat (i.e., dechlorinate) it first? Another possibility would be ammonia poisoning, as it will also burn the gills, but it generally takes longer to build up to deadly toxic levels than chlorine.

And I’m guessing your fish with long tails were either butterfly koi, or, more likely, shubunkin goldfish.

Hope this helps.

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