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It seems every time I check my tub with a test strip that the chlorine does not register...I add after every use which is every night. About 1 1/2 tsp...I'm wondering if I need to add more Dichlore at night when I get out so I get a good reading the next day?
...But if I can maintain a proper/constant level of sanitizer then what does shocking do? Does overdosing/shocking the tub kill off stuff that a proper level of Dichlor won’t?
If you haven't read it already, the Vermonter post in the FAQ on Doc's site (rhtubs.com) addresses this in detail. The main reason to shock was addressed by Bill and Vinny: to oxidize the combined chlorine (chloramines) and any other organic material present in the tub. The chloramines create what everyone associates with "chlorine smell", but provide no sanitizing effect. Shocking frees up the chlorine to do its job again. This can be accomplished with either Dichlor or MPS, but I prefer Dichlor for the reasons you stated (get both oxidation and sanitation) , and one less chem to store. The "supersanitation" of a chlorine shock, is a side benefit, and at least in theory could help kill off any chlorine resistant organisms that might be present. IMO the main benefit of MPS is that you can enter the tub shortly after dosing, while a chlorine shock requires several hours before levels drop. You should also be aware that MPS has a low pH, so regular use may cause your pH to drift down over time. It may also increase your TDS.