I'm sad to say we lost three of our Koi last week.
On Thursday we noticed the fish started swimming to the top, but they were moving much slower than normal. Many stayed at the bottom. This is something they do when it gets hot. Our pond has a lot of sun exposure, so it's not uncommon for the fish to hang near the bottom where it's cooler.
Yet our concerns started when one of our large Koi kept hanging at the top, near the edges of the pond. He was swimming slow, turning over to expose his belly. Then another did the same thing, this one having a twitch to his movements. They were aimless in their movements. If you're familiar with these fish, they know where they're going. They get friendly with you, sometimes will even eat out of your hand.
We knew something was wrong because they were moving around like they were blind. It was sad to watch and my husband and I felt so helpless.
Billy had just cleaned the filters, days before. He tested the nitrates and they were fine. Within two days we lost three large Koi. Beautiful fish. They have a personality all their own. It was a sad loss. Billy did more research and realized we had high levels of ammonia. This is something we will have to continue to treat due to the excess of fish we're housing in the pond.
All is better now. The fish are eating like normal and are moving around as usual. For this, I am thankful. And I'm impressed by my husband's care and perseverance in not relenting until he found the solution to the problem.