Is your pool starting to look old?
Are you starting to see discoloring or spots on the interior of your pool?
About every 5 years you need to have your pool drained and cleaned. Over time, with the weather, usage and chemicals being added to the pool, it builds up a high total dissolve solid base. Total dissolve solids can cause your pool to start to stain over time or to have severe algae growth. Pool draining and cleaning is required to keep a properly balanced water chemistry. Even if your pool looks fine after 5 years you need to do this to prevent from staining. If there is no staining, then you would just need a pool draining and a pressure washing of the interior of the pool.
Having algae problems that will not go away?
Then maybe you need to have the pool drained and chlorine washed. The third option would be for stains on the interior of the pool. You can have the pool drained and then acid washed. After these tasks are complete then the pool would need to be re-filled and the water chemistry balanced.