I have the Taylor test kit, it always says I have a pH around 7.3 - 7.5 but when I take it to the store, the stores readings are always about .4 higher than my readings and my Cl readings are always 1-1.5 points lower than theirs, then again, i am looking at shades of pink and yellow, how accurate can that be vs. a computer. Should I shock with bleach or with the SWG?

I live in canada so my swg is only active 5 months of the year. or should I shock bleach it instead.