Sounds like you may have high CYA. You can manage the pool without draining but fighting Mustard Algae will take a lot of chlorine.

Take a look at Ben's Best Guess Chart - this is the framework for understanding how you'll need to operate.

You'll also need (no substitutes) a Taylor K-2006 (or K-2006C). If you buy it through the links in this thread the Poolforum get a few shekels to keep the lights on.