I have a very large spa that takes a very long time to heat up. The deep end is six feet deep and the shallow end perhaps just about three feet or less. Cold water from the bottom of the deep end travels via the bottom drain to the pump/filter/heater. The heated water is returned to the shallow end. Surprisingly, there is not too much mixing so that shallow end can actually heat up fairly quickly so long as the jets are off. The deep end stays quite cold, especially the deeper, denser water. This temperature separation can be even better controlled, I think, with some type of "boom" between the shallow and deep ends. I was thinking about a shower curtain with weights at the bottom type of arrangement with a hole at the bottom of the curtain to allow for the retention of hot warmer water at the surface. Thus, there would be a warm end and a cold end. Has anyone heard of this sort of thing being done, and if so, can you provide some insight? Thanks.