What does the disc look like? I could not see anything. If I hold the header up to the light it looks like a straight through tube. Perhaps they sent me the wrong item? In any case the way I have it now I am flowing water down the length of one panel into the far end of the other and back up to the top where I take it off to the pool. IF there is a disc it is not doing anything as the panels are realatively cool the entire length. When I did it as they suggest the first panel stayed hot and the second was cool - so I know that was not good.