wow he must have loved his work and nice looking fish ,You may need to think bigger for a pond a a lot of filtration as koi produce a lot of waste and that could be what is causing your problem plus the hot temps .I know my son lives there and he said it has been hotter there than here .I know he works for a metal welder in Perth Amboy and lives in Edison off Woodbridge Ave.near the Highland Park border .He lives down near the Green Derby .
Ask your son if he's ever heard of Frank Timco... he owned the iron works in Perth Amboy and built my home. he died about 12 years ago.
I'd love to build a bigger pond and have been contemplating it for years. just need to pull the trigger. My goal would be at least 3000+ gallons
I overfilter the current 900+- gallon pond to try to compensate for the high load. I'm using a Laguna Bio Falls 5000 fed by a Max Flo 2400 pump on the bottom of the pond, plus a skimmer with a powerflow 1200 into a Laguna Pressure Flo 2400 with a 20 w UV. The pressure flow also dumps into the Bio Falls before returtning to the pond via a waterfall. 20% water change every week, plus an occational 50% + change. All water parameters are spot on and water temp hasn't gone above 74 degrees F.