Re: Above ground clorine question
Use 3" tablet, in a floater, for your ongoing chlorination. You can get a bucket of them at Costco for pretty reasonable. Use 6.5% generic house hold bleach to shock the pool. Your 18 ft'r is probably about 9-10,000 gal's. Use six gallons of bleach, to shock, at the beginning of the year, maybe once or twice during the summer and at the end of the season as you are putting the pool to bed.
Also use and algaecide periodically during the season, at the beginning of the season and to winterize. You shouldn't need to add anything between Dec and Aprilish.
DO NOT BOTHER with powdered shock chlorine. Especially if you get a case of algae at the beginning of the season or any time in between. The algaecide should keep any growth away, even with heavy use and high heat, during the summer. Just be sure to keep your tablet chlorine level up.
Tablets are for ongoing because they last a while and have a chlorine stabilizer in them. Sunlight degrades chlorine rapidly. That's why you can super shock it with liquid one day and go swimming the next. Too much stabilizer and it locks up the chlorine. You'd get a reading but it wouldn't be doing anything.
Follow this perscription and your water will stay crystal clear.
