So I have a 4500l, 1000 imp gal pond. Home made filter with 2 pads, 1 wool filter bed showering on 1000 bio balls and volancic rock. In addition i have a 60w uv, 7000l/ hr pump, a twin air pump and a small solar air pump all under the medit fizzing away. The water enters the pond 18inch height so good airation. I have 8x 6 inch koi, 10x 3-4 inch koi and 6x 4inch goldfish. My pond is well established 18 months. Nitrite 0, ph 7.5 ammonia though is 5ppm and has been for at least a month. I would think that my filter is being over worked and my pond is overstocked but the pond originally had 15x 12-15 inch koi (I had a very unfortunate plumbing issue and lost all but 1 fish ) back then the ammonia levels were 0 so I know the filter can handle the stock. I haven't lost any fish they seem happy and healthy. I have reduced my feeding and changed to a wheatgerm and I also have a lilly which is doing OK. No algae blooms. No smells. No run off. What's going on? Am I dancing with the devil?