I drained the water about 4 inches below the return. That's about 17" below the top of the wall. Instructions said between 14" and 18". Before the rain it was fine. The leaves would sit there nice and dry and simply blow off with the wind. Now that it has rained, the water has pulled it down to the water level and it is sitting in/on the surface of the water. It's like the rain water doesn't drain through the cover fast enough. So it puddles and weighs it down. I am pretty disappointed with this product thus far.