Here is the article to Cycle your salt tank
You definitely want to use RODI
water for the tank and all PWC
's (partial water changes) and for evaporation replenishment.
Don't bother testing pH during the cycle. You want to see Ammonia go up and then down to ZERO, followed by the same for Nitrite. Then nitrite should drop to 0 and nitrate should rise. PWC
's remove nitrate.
You have LR
in there which is great. If it was uncured LR
or out of water for more than a few hours it will be your source of ammonia for the cycle.
You don't want to use Prime or similar during the cycle.