Hi all . My first post and hope you can advise . Have an outdoor 12000 gallon swimming pool that I converted 15 years ago to a fish pond and have 6 large Koi about 18”+ and 15 or so small goldfish and Koi . The large Koi have lost there appetite , weather is cool at present and the ph is about 7.5 / 8 . The water is unusually clear and they are congregating at the shallow end . I have plants all around and have a large filter . I occasionally run a water change from a large lake I have on the property ( I pump out pond water and pump in lake water at the same time ) the fish love this lake water and they sit under the lake flow coming in , so I assume this water is better than the pool water as they love it . I see test kits are available to test for all sorts of things but have only tested for ph , should I test for something else ? Richard