• With large dark rocks, they created the walls of the pond. They also placed gray tiles on the floor of the pond. All stones used were dark gray to collect the sun’s heat and warm the water naturally.

  • Their next step was to fill the pool with water and let the earth and dust to filter by purification systems.

Source: https://www.reddit.com/r/DIY/comments/21l6te/we_made_a_swimming_pond/