The better question is how many ppm of FC are you trying to get to? Most people don't have a clue. The pool store/installer told them to "add two of these once a week" and they've been doing it since whether it needed it or not. Formula, FC (free chlorine) + CC (combined chlorine)= TC (total chlorine) Always. Shocking a pool is simply raising the FC level high enough to destroy CC so in fact CC determines whether or not you should shock your pool. So, If you have a FC level of 3ppm and a CC level of .5 or less then shocking really isn't necessary. Now if you have a FC level of 1ppm, a CC level of 1ppm then shocking would be necessary. A General rule is anything above .5 cc indicates shocking is in order. How much chlorine to be added depends on your CYA/Stabilizer level. See http://www.poolforum.com/pf2/showthread.php?t=365 for Ben's Best Guess to determine this. So if your CYA is between 30-50 ppm you could shock up to 15ppm. My experience has been that I never really have to go this high so I usually shoot for half initially and it works unless there is something really chewing up the chlorine (i.e. algae, lots of "junk" etc.). Look at the water, if it is otherwise clear, the "full dose" probably isn't necessary. Now, the great thing about using bleach is 1 gallon of 6% bleach raises the chlorine level in 10,000 gallons of water 6ppm. Plus, mwsmith2 (Michael) has a great calculator than can help you determine how much to add as well. Go herehttp://www.poolforum.com/pf2/showthread.php?t=1652 , scroll down to the second post, click the link next to Get BleachCalc 2.6.2 here: to down load it. It is wonderful. If you have further questions and or problems, post your pool type, size (how many gallons), and reading for FC. CC, PH, ALK, CH and CYA and I'm sure someone here on the forum can help.
Bookmarks