The main way to determine whether you need to acid wash a pool is whether or not the bottom of the pool is visible. Algae may proliferate, if the winterizing was done incorrectly or the pool has been allowed to stagnate.
When the bottom of the pool is visible, an acid wash isn't necessary. Instead, clean it with three things:
Acid Wash Swimming Pool
When the pool's bottom isn't visible, cleaning with chemicals isn't as effective and it usually costs more than the price of acid washing the pool. Also, it will require a lot more time to try and clean it. The algae growing in the pool creates stains on plastered walls, so that an acid wash is recommended.
Another reason is to rid the pool of stains:
Removing these will refresh the pool's look, making it cleaner and brighter in appearance.
The acid wash strips off a thin layer of the plaster. The majority of plaster coats exceed a 1/2-inch measurement. Stripping a bit away isn't harmful to the pool walls, if done with care. It shouldn't be done annually, or re-plastering sooner will be necessary. However, an acid wash can be done several times before re-plastering is required, when done correctly.