We need to drain our pool to reduce the CYA level. We also have some patches of algae on the sides of the pool. Is it recommended to spray or treat these patches when the pool is drained or will drying and exposure to the sun finish any living algae? Is all the CYA removed with the water that is pumped out or is there a recommended rinse or cleaning procedure for the exposed walls to clean out all the CYA? Thanks!