I inherited a pond when I purchased my new home. It's about 800 gal. with a waterfall that drops about 2'. It loses about 40to50 gals. a day. I've patched and plugged every hole or crack I could find. When I have it off there is no water loss from the pond the filter or the plumbing. It only looses water while the waterfall is running. What is an acceptable amount of water loss per day?