catchment cover

[MarkP]

I bought three 10' x 20' shade clothes from Ace Hardware and criss-crossed them over the center of my 15' diameter tank to get full coverage as well as getting extra thick coverage over most of the tank. The nature of the cloth I got from Ace is that it is quite stretchy like a new sock when the elastic is still good. I am able to pull it down tight and it seals over the edge of the tank perfectly and is stretched taught across the top. It hardly sags at all. I have a 2' x 2' x 1" piece of styro-foam floating in the center of the tank that holds up my floating pump suction. Sometimes when it is raining, the tank is full, and the cover is heavy I can see the outline of the foam square under the cover but I never see any ponding. The foam square is tethered so that it stays in the center of the tank with monofilament fishing line and stainless steel counter-weights. The tethers need to be long enough so that they still operate when the tank is almost empty so basically each tether is long enough to run from the lip of the tank down to the bottom and across to the float in the center. The weight goes where it will hang near the bottom of the tank when the water is that low. For a tank 7' tall and 7' radius that is in the middle of a 14' tether.

I honestly think this is a better cover set up than with the frame. It is literally bug-proof. It holds itself up well enough, the measure of that being whether there is ponding when the tank is full and the cover is wet and heavy.