You can go online at Costco.com and apply for a Costco Membership there by adding it to your shopping cart if you are shopping for the first time. Your membership card will be mailed to you within 7-10 days but you can actually shop at the online store immediately.
The three most common chlorine-containing substances used in water treatment are chlorine gas, sodium hypochlorite, and calcium hypochlorite.
Chlorine or bromine-based sanitizers must be used with UV light. UV is effective against germs including chlorine-resistant parasites like Cryptosporidium and Giardia, but it must be used with chlorine or bromine for residual sanitation. UV systems work by circulating pool water past UV lamps, where germs are destroyed.