Repainted pond fish dying

[Stephen Noble]

My sister has 14ft by 6ft deep cement pond filled with orfe/ very large koi and goldfish.
We repainted using professional pond sealing paint (£150) a pot. Did everything it said, washed it down after drying etc.. put fish back in and now they’re all dying so far out of 21 fish she has about 4 goldfish left and one ghost koi. It’s so sad all the fish she had had for years and well over foot long.
She tested the water and niterate etc we’re fine. What went wrong ???

Are you sure the concrete was completely coated and no spots were missed? And, where and how were the fish housed during the repainting? I wonder if the temporary housing was the source of the problem.
Stephen

 

[Mossey00]

The temp pool was 10ft by 3ft and she put pumps and air pump in, as well as the pond water, if it’s the catyalist of the paint what can she do ?

 

[MitchM]

...
They were kept in a 10ft pool with the original pond water and moved the pump into that. The levels were low/med on ammonia and stress, ph and gh were 12.
...

PH and GH were 12?
Could you please list all of your numerical water test results, separately?
Also, what was the name brand of the paint product you applied?

 

[Jhn]

PH and GH were 12?
Could you please list all of your numerical water test results, separately?
Also, what was the name brand of the paint product you applied?

Hopefully she meant kh not ph, since her fish wouldn’t be alive in a ph of 12.

However, if ph is elevated, along with temp that could make ammonia at .5, toxic enough to do in already stressed fish.

Could be epoxy paint, but if paint is not outdated and directions were followed seems less likely. If it was designed for pond use.

 

[MitchM]

I expect that's the case (kh, not ph) and my next questions would be around what happened during fish transfer. 12 kh and gh is pretty high so if they came from neutral water, they could have died from PH or osmotic shock.
I haven't yet considered the other items that were added to the new pond.
The OP says old water plus pond water was used, don't know the % of each.
Just waiting for clarifications on water quality.