Creative! Mike, is that Offbreed right?

Jim

"Offbreed" wrote in message
...
Mike Patterson wrote in
message . ..
I have a 1200 US Gallon pond with an overflow spillway at one end.

If I fill it up, it seems to hold it's level fine, but after a really
heavy rain (we got about 3 inches in 4 hours a couple days ago), the
water level after the rain was about 3-4 inches LOW.

Over fill and watch around the edges. I'll wager that part of the
sides is not properly supported and the extra water causes the
membrane to flop down. Once the water level drops enough, the membrane
stiffness makes it come back up where it belongs, and you have less
water than before.