[fred cook]

I have had a concrete in ground pool for about 15 years. Initially, it used a chlorine/cartridge type filter, but about 3 years ago I switched to using a salt/sand system. The salt/sand system is much easier to maintain with lower chemical costs. Under normal conditions, all it needs is the addition of an occasional bag of salt that is poured directly into the pool. Cleaning the sand filter only requires a backwash and rinse about every 2 months.