We choose to leave our pool up all year, uncovered. by the time summer hits, we have a MESS!! We pressure wash the sides and the bottom. This year the sides came pretty clean, but there's dark algae still on the bottom. It would take hours to get all that off the bottom. We chose to leave it and are currently filling it up. The pool is about 4 1/2 feet deep when full. How can I clean that stuck on algae off the bottom? What chemical would eat that off? We also don't have a vacuum, as the one that we use that came with the pool is not good at all. do I need to buy one that people use for a built-in pool? We hope there is something that will kill that stuck on algae and we will just empty, spray the loose algae out, and refill.