hi all, i have a well established pond, had it for about 12 years now, it measures 14ft by 9ft by 4ft deep and holds about 3145 gallons i have two large filter boxes, a uv clarifier and a submersible pump which shifts about 3000 gallons an hour it also has two smaller pumps powering two waterfalls. the fish i have in it are koi, goldfish, orfe, 2 barbel and 2 catfish. we used to have really clear water but the last 2 years in late summer the water has turned very green and cloudy and has a lot of particles in it. the pump is checked twice a day for blockages. about 3 years ago the goldfish had babies, about 20 of them and when they grew to a reasonable size i gave all but 2 of them away. i dont think the pond is overstocked, all the fish seem perfectly healthy but this cloudy water is driving us nuts. has anyone any idea what might be causing it ? my partner insists each year that we empty the filter boxes out and clean the media and the water does improve but i'm sure by doing this we upset the biological balance of the filter and as i'm now suffering from arthritus it's also becoming a pain in the backside each year. if anyones got any suggetions on why this is hapening and how to stop it i'd be grateful.