I bought a new house this year and it came with a large Koi/Carp pond and lots of fish. Just recently they got infected with gill flukes and parasites and probably some bacterial infections. The fish in the worst state of health was unable to swim straight and over a few days he got worse, floating like he was dead. Everyone told me that the best thing to do was to put him out of his misery so I decided to take him out and ozonate him in a smaller roughly 50 liter container. We’d ozonate for an hour at a time with a break of two hours, and then repeat this process 4 to 5 times in succession. Then we put him back in the pond and did it all over again for one more day.

The interesting part was that we had an oxygen air stone and a different air stone with ozone both bubbling in the container and he swam to the ozone air stone and laid there with his fin on the tube. While he was lying there, I used the magnetic pulsing unit on the other side of the tube.

Long story short, we put him back in the pond and he is now completely fine! We also ozonated another fish that started to go wonky and he is fine now too. One more fish that wasn't looking well, we didn't ozonate as we were going to wait to do it upon cleaning the whole pond on the Tuesday. A hot Monday sadly saw him dead when we got home from work that night. This makes me feel even stronger that the ozonating helped the other two.

Months later, the two fish we ozonated are amazingly fine. I believe the ozone is great for Koi with viral and bacterial issues. They seem to know when they have had enough too as, when in a smaller container they tended to go in varied times from laying over the air stone to keeping far away from it - which is when I took them out. My neighbor who has had Koi for 30 years can't believe the one that was the worst is still alive.