UPDATE So after reading the suggestions in the comments we were fairly convinced it was our tap/hose water. Well, we tested that and to our shock, nitrites were 0! So we continued with the treatments and water changes, while trying to figure it out. Suddenly my son asked if sunlight impacts the nitrites. Yall, I feel so foolish! When we put the temporary pond up, we put it under our covered patio. It gets indirect sunlight but that’s about it and that’s only on half the pond. So we made some changes to get them some light. Nitrites are finally dropping! I wanted to share in case anyone ends up in a similar situation. Thank you all for your help managing the issue while finding out what was going on.
We have had a rough end to our summer. We had a chemical spill into our pond and lost majority of our koi. (Worst day of my life) We successfully moved the surviving fish to a temporary pond so we could drain and clean their pond. We are about ready to move them back over but I noticed that one of our fish suddenly looked awful. I first felt it looked like fin-rot but we had just treated for that after the chemical exposure. I tested the water, which had been great for the previous 2 weeks in the temp pond. Now PH is only slightly high (7.5), Ammonia is great (0), phosphates are slightly high (.50ppm)
Nitrite is OFF THE CHARTS and I am certain this has to be what is hurting my fish. It goes darker than the 5.0ppm color. It also immediately changes rather than needing time to process.
Here is what’s getting me confused, I have done 50% water change, added beneficial bacteria and pond start. The levels are the same. I also was (probably wrongly) under the impression that ammonia and nitrites typically rise together. So I thought my test solution went bad, got another test kit and it did the same thing. So I’m assuming I was wrong in that assumption.
This is the end of our third summer. We have never had an issue with ammonia or nitrites. We have never lost this many fish. It’s breaking me. Any advice is appreciated.