Neat idea Eric, I bet you could use black shade cloth it comes in 6 ft widths from HD and Lowes to form the center areas and then put the peat on top of it. It also would cover the pvc pipe. Might try a little 2' by 2' in the koi pond and see if it works and if it does make a larger one in the .4 acre pond. I was thinking of building the frame in a square and use some t's and a cross coupling to make a "+" in the middle for extra support then drill a few 1/4 inch holes in the pvc and then using a can of expanding foam to fill the pvc. Then place the shade cloth over it and stitching it to the frame around the perimeter with 130 pound dacron fishing line. Sure would be alot cheaper. What do you think?

Bob