Heating a swimming pool with Fresnel Lenses is possible but simply pointing one at clear water does nothing. A dark target is required to absorb the concentrated sunlight. Fresnel Lenses do not amplify light, they concentrate light. An obstructions blocking the path of natural sunlight light a lens simply redirects light from a larger area to a smaller area. The better option is to sink large dark objects to the bottom of your pool where sunlight can expose the dark object. Square area is square area so a one meter square Fresnel Lens concentrated to a dark target in a swimming pool will collect the same amount of solar energy as a one meter square black sheet of plastic or metal. Since the objects are submerged, metal and plastic are equally as effective due to equal surface area in an aqueous bath. Assuming the surface is equally matte.
Youtube is deleting a lot of our videos because we used Royalty free Garageband music in the background. People are using the Garageband loops to make professional music and adding to the youtube content ID program so even though the Loop is 100% royalty free from apple and our video using the loop was released in 2008, a musical artist can copyright the royalty free loop in 2013 and zap our video. NOTHING WE CAN DO but take down the old video and replace with no music.
Pick one paste into youtube with the quotes, if you are familiar with Apple Loops you will be surprised
"Hans Bolex-Samba Cubano - Music Of The Sea"
"Steve Hogarty-Bailando Hasta El Anochecer (Dance Until Daylight)"
"Bobby Cole-Confused And Clumsy"
"Bobby Cole-Down At The Salsa Club"
youtube search "Alvaro Vela-Dharma" this is an apple loop royalty free.