I'm not to concerned about my plants, but don't want to kill my fish. I've got two large bio filters that I keep clean, but I continue to have mucky water. Anyone know of a high powered product that will really work. I know I can drain it and add new water, but I have a 3500 gallon pond and it's a pain to do , so if there are any expects out there that knows of a great product that works really well and fast. I would be much thankful for the information.