In an effort to keep the pool water warmer, I am following the method others have described here of placing 4x8 sheets of DOW brand Blue Styrofoam Insulating Board under the liner. The sheets of foam are taped together with Gorilla brand duct tape.
The idea is to provide some thermal isolation between the pool and the ground. It is my understanding that other than controlling evaporation with a solar cover this is the next best thing one can do to keep the water warm.
Some have described placing a tarp between the foam board, and the liner...
What if any benefit is there in placing a tarp over the foam board and under the liner???