Have a 1,000 gallon fish pond and have had for 6 years with no problem. In last 2 weeks have lost 3 koi. I have treated the pond with a 7 day treatment of Knock Out. The pond water PH was high (9 i think) so I have put recommended stuff from a local pond store and it is down into range now. This am I have another fish floating on side and swimming with it's head down. I was told not to change water out it would stress the remaining Koi too much. Any suggestions on what could be wrong that I can correct. This is the first time we have ever had any problems with our pond. Also want to mention that my trouble started about 4 days after I found a live baby coon in our back yard, not sure if this would have anything to do with it.