Welcome to the forum, go ahead and put your cartridge in. Get yourself a testing kit, too.
Sometimes you may have two 'chemicals' out of whack, when you correct one the other falls right into place and it seems pH is one of them. Don't quote me on this but if your Alkalinity and pH are both off and you get the alkalinity corrected the pH falls into place. I have that problem when I change water, pH is sky high and the other, I think alkalinity, is off. I correct the alk and pH magically corrects itself.
Remember it may not be alkalinity that I'm thinking about, someone else will correct me if I am wrong, so don't go out and mess with your alkalinity until someone else confirms or refutes what I'm saying. :-/