My pond has been perfectly healthy for a year. I had a bit of algae bloom, so I have been cleaning the filters every other day or so. Three nights ago at 3am my fish were spawning madly and happily. At 10am, one fish was dead and five more were dying. Water tested perfect -- hard and a bit alkaline, but that's normal. All fish were acting odd, hovering around the bottom, not eating, one was swimming in insane spirals from top to bottom. No more spawning. Not knowing what had happened, I immediately overreacted and medicated with Melafix, Pimafix and, because the fish seemed to be covered with bubbles, malachite green in case it was ich (it probably wasn't). I set up the hospital tank and salt bath tubs with pond water and isolated and salt-bathed the obviously sick fish. The next morning a filter malfunctioned and dumped about half the water, so I conditioned and replaced ~600 gallons. I did not medicate the new water. The fish remaining in the pond seemed better. The fish in the hospital tank all died. One fish in the pond was floating on its side. The turtle tried to take a bite of its head, so I removed it to the now-vacant hospital tank and began salt baths. The fish appeared to be paralyzed from the pectoral fins down. It can move the pectoral fins and it breathes, opens it mouth and its eyes follow me. It floated on the top the first day, and has been lying on the bottom since. I expected it to die, but continued the salt baths and have lifted it to the surface a few times a day to ensure oxygenation, although the filter should make the water viable. I think there are two possibilities. In cleaning the filters, I replaced a new piece of filter medium with a used one I liked better, but which may have become contaminated, or since the tree over the pond is blooming, it may have dropped something into the water. Whatever it is, today when I put the fish in her salt bath, she moved her tail fins and swam a little! (I arbitrarily assigned her female gender.) She repeated the little swim movement when I put her back in the hospital tank. Since I thought the old pond water may have been contaminated, I changed out both tank and tub with fresh clean pond water. I also propped her up with a net so that at least she's vertical rather than lying on her side. Is there anything else I can do for her? I'm desolate at losing the others and desperate to make her well. BTW, the remaining fish in the pond seem to be recovering well and the turtle seems unaffected by the entire ordeal. Sorry this is so long. Thanks for any help.
