I have a 22,000 gallon koi pond which has been stable for 5 years.
Today fish are swimming near surface NOT gasping for air.
Water test reveals all parameters normal except pH which is higher than 9.

Fish looked absolutely fine 12 hours ago.
Have applied "pH Down" at 50% of recommended dose.

One fish has now died.

All suggestions welcome.

Hi,

You should go for some big water changes urgently. If you can you should move your fish to a temp holding setup.

Best of luck.

ara,

At what time of the day did you test the pH?

Try and find out too what caused this high PH all of a sudden??? Can it be source water???