Etching is a problem encountered by pool owners with low calcium hardness or pH, where the pool water becomes corrosive to concrete, stone, or metal surfaces exposed to the pool water.
What is Etching in swimming pools?
Etching generally refers to a process which cuts into the surface of an object or solid material, leaving a visible area of removed material. Etching can occur a number of ways; by use of a strong acid, high pressure water, laser or similar directed energy, or with a metal or diamond-tipped cutting tool. Etching too deep into the material can expose the underlying material to corrosion or become structurally weakened. Intentional etching is usually performed to create a design on the material surface, but natural etching is usually referred to with a negative connotation.
For swimming pools, etching of any kind caused by exposure to corrosive pool water is undesirable. Low calcium hardness in pool water can etch the surface of concrete, plaster, shotcrete, and gunite pool walls and floors. Cement, masonry, grout, stone, and tile are also at risk, where the water will actively seek to replace missing hardness with calcium and minerals found in the surrounding pool materials exposed to pool water.
Low pH can also cause etching both on concrete and stone, but also metal surfaces. Pool equipment, railings, ladders, pipes, and fittings are all at risk of corrosion with acidic pool water caused by low pH. Metals can dissolve into the water, turning the water cloudy and increasing the risk of pool staining.