black pond water
Background: I have an 11'x 18' pond that is 3 feet deep with a small creek and waterfall. I have a submersible Oase Powermax 15000 pump and an Oase Bio Clear 10 filter. I figure a surface area of 26.3 ft(?)- no bottom drain. I have about 32 goldfish, a couple of Shubunkin and 2 Wakin. The pond has been up and running for seven years--with tiny fish at first, now they are about 6 to 8 inches in length. I clean the filters about every 6 weeks. Unfortunately there is a huge, beautiful maple tree right next to the pond. I skim the leaves off the pond as best as I can and this year I bought tree netting to cover most of the pond and catch what I could but always some fall into the pond and sink before I get them out.
Problem: This year my husband helped me and we took the netting off and the water looked BLACK and I couldn't see any fish at all. The filter was really clogged with muck--as usual and as usual it had been 6 weeks since I had cleaned them. I thought all my fish were dead and felt just SICK. I cleaned the filters (4 fine and coarse filter foam pads) and tested the waterI have a slight upward slope I can only overflow the pond to dilute the water which I did. The ammonia level was 3.0 mg/l and pH 8.5, but fish are still alive--What caused the black water and how can I stop this whole problem from happening again? There is a lot of muck and leaves and pine needles on the bottom of the pond, built up over the 7 years, even though I try to skim off the surface frequently. I don't know how I would ever get all the fish out or what I would put them in If I drained the pond--HELP please as I really am attached to my fish. By the way I have water lilies, and water iris and some unidentified rushes growing in the muck and thriving actually.
I would greatly appreciate any help or suggestions.