Same holds true for any plaster. 2%-3% ratio of calcium added to a mix acceptable by most of the manufacturers. Anything above that ratio can create a bleed of the calcium through the finish. If the calcium level is low in a pool, the water is considered aggressive because it is soft. To "satisfy" itself it may pull the calcium from the finish to make the water "harder". Scale may occur also.

It's also super important to add a sequestering agent upon filling the pool to combat any minerals in solution form and prevent them from becoming solids and attaching to the surface. AKA scale.

There are some chemicals to to try to eliminate existing scale to help renew the finish.

Sometimes a light acid wash can clean the surface but you have to be careful on the strength of the acid so you don't etch the surface and make it rough.

This is why it is paramount the moment the pool is filled to begin chemical treatment and going forward for at least 30 days after to ensure chems are stable and the surface is sound.

Most plaster failures are due to chemical treatment.

I need to clarify last line statement. Failures are due to improper chemical treatment.