The costia attacked my fish without any forewarning symptoms and before I knew what was happening I had quite a few fish in my pond in serious distress.
I apparently missed the first symptom and brushed it off as a spawning injury. It was a fish that I purchased in January 2013 and kept in quarantine until late November 2013 before putting her in my 17,000 gallon flow through pond. She appeared to do well until this spring after a spawning incident in my pond. She lost eggs and then started to hang out near the air stone. Then she seriously started to loose weight and even muscle. I just thought she had a serious injury from the spawn and would not recover. At this point no other fish of the many in this pond were showing any symptoms. No flashing, not jumping, just their usually swimming and eating.
Then suddenly about 6 more started to hang out near the air and I saw the typical patches and red streaks in the skin and fins and immediately recognized it as costia, since I have had it 3 times in the last 20 years. The first time was in imported koi after 6 weeks of quarantine. The second time was in 2011 in this same pond.
I saw the symptoms in the 6 additional koi too late in the evening before I had to go to work early the next AM so I could not treat until the next afternoon. All I had on hand for a 17,000 gallon pond was potassium permaganete. I treated with a fairly heavy dose and left it in 3 1/ to 4 hours before the koi all became extremely stressed so I had to neutralize it. This seemed to knock things back quite a bit and fish seemed somewhat improved.
I ordered Terminate (they say same as Proform C) and there was a delay in the order. So due to the fact that the koi were so stressed by the PP, I thought it was possibly due to imbedded costia in their gills. I managed to find some Trichloricide in the basement and treated the pond with it. The next day most of the fish looked better.
Since Trichloricide is no longer a favored pesticide, I waited for the Terminate to arrive. The first dose all was well. The next day I added the second dose. At this time only 1 koi appeared severely stressed and was still hanging out by the airstone. I checked before I went to bed after the second dose and at 333 AM before I went to work and all appeared well. Fish just cruising around the pond.
When I got home at 333 PM all of my fish were close to dying. All piled up on each other over the air stones. I am not sure why the second dose depleted all the oxygen, but apparently it did. I added more air and started the water back on the flow through. In summer this is probably at least 5,000 gallons per day.
I have lost some koi, a few the day before the treatments started. A couple after treatments started and then some yesterday during oxygen depletion. Several of these were some of the largest, but there were all sizes even down to some of the smallest, so I am thinking it was because of damage from the costia as well as low oxygen.
I would think these treatments have knocked the costia back pretty good, but I wanted to do the last treatment of the terminate, which should have been done yesterday. I know I should not add anything else today. I am not sure even how they are doing at this point since they have gone to the bottom of the pond, but they usually do this when it is hot or warm in the summer. They hopefully will come up around 5 PM as this is there usual procedure at feeding time. While the pond is fairly clear at the surface, I can only see down to about 3 foot at the moment.
I need thoughts on what to do next.