The idea is to lower your PH, TA, and CH levels enough that you start dissolving calcium off the walls and floor of the pool. If you have a pool heater it is important to either completely disconnect the heater or keep PH above 6.8 while doing this. Also, you don't normally want to swim when the PH is below 7.2. If you do this, you need to carefully monitor the process. You don't want it going to far. At the same time, it can take quite a while to have the desired effect.
To figure out how much you need to lower PH, TA, and CH you can use the Pool Calculator to calculate your CSI. You want to lower them enough that CSI goes down to between -1.3 and -1.0. As the scale on the pool dissolves into the water PH, TA, and CH levels will come up, so ongoing effort is required to keep them low enough.
The alternative is to do a full drain acid wash, which means draining all the water out, and manually washing the pool surface with muriatic acid to dissolve the scale. This is much faster but also far more work and requires some skill to apply the acid uniformly enough that the proper look is achieved and nothing is damaged. This approach is best when the scaling is not uniform to begin with. Manual applicaiton of acid allows you to remove more scale from areas that require it and less from other areas.
