Solarpills?

[veghead]

Do they harm your pool?

[BigDave]

Do you know what's in them?

[waterbear]

they are not harmful and are basically paraffin and an undisclosed fatty or waxy substance dissolved in isopropyl alcohol. (Isopropyl alcohol is the only dangerous product listed on the MSDS since it is toxic. FWIW, both 70% and 99% isopropyl alcohol are commonly sold as 'rubbing alcohol' at the corner drugstore so if you don't drink the liquid inside the pill or fish you are fine. The product in all these pills, fish, etc. is HeatSavr Liquid, which is sold by the gallon for commercial installations and is dosed with a peristaltic pump, the idea it that it forms a waxy or oily layer on the surface of the water that (they claim) is only one molecule thick.
IF the surface of the water is perfectly still (such as an indoor pool with no water movement or air circulation with all pumps shut off overnight) then a best case is that the liquid can retain perhaps 6 degrees of heat that would otherwise be lost by evaporation.
In an outdoor pool that is subject to wind currents but the pumps are off it might retain a degree or two at best.
If there is water circulation it cannot form the protective barrier to prevent evaporation heat lost.

General consensus is your money is better spent on a solar cover instead of the pills or fish.

[veghead]

Well, maybe we will put a solar heater on the roof and call it good.

[BigDave]

Solar heater on the roof plus thermal blanket - not good, awesome at no incremental cost.

[chem geek]

HeatSavr is most likely described in this patent which indicates that the product is just a combination of "an aliphatic alcohol component having from 12 to 24 carbon atoms per molecule" combined with calcium hydroxide. The calcium hydroxide is just a carrier and dispersing agent.

The preferred embodiment uses cetyl alcohol (1-hexadeconal) and it only takes a small amount as the layer is only one molecule thick. Another product, WaterSavr, appears to use stearyl alcohol. Yet another uses a combination of the two.

Such products only work moderately well if there is no wind. Possibly better than nothing in some cases, but no where nearly as effective as a regular solar cover.