Help! I recently had to build a new 6,000 gallon pond because my mud bottom pond with only a fountain for aeration started to leak badly. All seemed fine until the transferred Koi and goldfish started to die. Water testing showed nothing extreme: pH-7.4. NH3-0.35. NO2- 0 NO3-5.0 . New pond has EPDM bottom, washed river rocks and 3 waterfalls with big pump capacity, bubblers and skimmer working. Lots of foamy stuff on top but fish number is small. Nets cover both pond and waterfalls and no debris is decaying in the pool. We have teated with beneficial bacteria, and antifungal products and water clarifiers. Fish continue to die. Any suggestions?