Quote Originally Posted by Phillbo View Post
Is there a calculator that will tell me how much 20 Mule Team to add to get my 21000 gallon pool to 50ppm?

Check out the Pool Calculator.

If you save the link to your local computer you can use the Pool Calculator when you're offline and they have apps for iOS devices. I've used it to calculate my pool's chem balances for several years with excellent success.