Is the liquid solar blanket called Tropical Fish still available?
Yes. Intheswim.com has them.
A blanket can help increase the temperature up to 10 degrees, a liquid blanket less than that. Used together you will still only see a maximum of 10 degrees but the liquid cover will help minimize heat loss while the cover is off and people are swimming. Unless there is some reason you can't use a standard cover like high swimmer loads or indoor pools where you want to minimize off gassing all the time…
Conversion from solid to liquid is called melting, conversion from liquid to solid is called freezing, conversion from liquid to gas is called boiling (or evaporation depending upon how quickly it is happening) and conversion from gas to liquid is called condensation; conversion from solid to gas is called sublimation.
When you heat something, you get to do from solid to liquid, and that called melting. The liquid to a gas its called vaporzation and evaporation. A solid to a gas its called sublimation. When you cool something, you get to do from gas to liquid its called condensation. A liquid to a solid called freezing. A gas turn straight to a solid called deposition.