. I cannot think of any reason to "shrink" your pool. If however you wanted to do this, it supposed it is possible by trimming the correct amount of aluminum border and buying a new (properly sized) liner. Good day sir.
20
56.52
About 28,944.8L
You should not put any Earth in your 18 foot round 5 foot deep pool. You should only put water and cleaners in the pool.
Circumference = 18 feet.Depth = not known.
fifty-six The circumference of an 18-foot circular swimming pool is: 56.55 feet
10000
About 7,600 gallons
fifty-six The circumference of an 18-foot diameter circular swimming pool is: 56.55 feet
Cannot be answered with only these measurements. You need to specify what shape the pool is. Also, for a rectangular pool, the length, width and depth are needed. For a round pool, the diameter and depth are needed.
An 18-foot round pool with 3 feet of water contains 5,734.8 gallons of water. If you fill it to 4 feet deep it increases to 7,646 gallons of water.
If that is 4 feet tall and 18 inches in diameter, it would be 16.83 gallons.