21' above ground pool Currently use Baqucil chemical and want to switch to Chlorine chemicals where do you start?

I'm answering this question based on what we did when we switched from Baqucil to Chlorine. We stopped using all of the baqucil products for a few days then only used 'htp' clarifier and algae killer (from Walmart) to keep the water from getting too green and too bad off. You'll have to test the water every day and only add the chlorine when your water is showing '0' or less on the baqucil products. It might take a couple of weeks to get back into shape, you even might consider using a 'chlorine stabilizer' product to quicken the process and TEST, TEST, TEST!!! GOOD LUCK!!!