Update... It has been 2 weeks, smartchlor cartiridge was set to 5 first week, but chlorine indication was low. Upped it to 6 and was fine for a bit... however my ph was running high. Put in more than twice recommended ph decreaser but did not come down enough. Then took out cartridge and realized it was about empty. Put in new smartchlor cartridge and next morning everything (ph, chlor, etc.) was great. Note that I did shock before putting in new smartchlor. In retrospect I think that my problem was I did not shock. I will be shocking at least once a week and maybe more if heavy use. Current use is about 5 times a week. Stay tuned. I really do not want to go thru 2 smartchlor cartridges a month ! I keep my temp at 101 degrees and my tub is 550 gallons. (Tropic Seas Tahiti Elite).