Well have had my pond for about 9 years...Have not been able to do a complete cleaning for last 4 or 5 years and with all the leaves from trees, the water was not so clean. I have never lost fish, but this year about 15 or so. Thought it was racoons, but now think it was combination of water quality and also a broken glass gazing ball in bottom. So pruned the trees and emptied pond. Didnt realize there was glass in the bottom and accidentally found I puncture the liner on the bottom. Couldnt find leak, but after putting almost 5000 gallons of water in three times I ordered new liner. Finally reinstalled and didnt disturb surrounding are too much. Fish should be back in next week and will be much happier. They have been in a 300 gallon tank for a week already. Expensive cleaning cost me almost 700 when said and done, but I love my pond and I am sure the fish want their 5000 gallon home back.