When I first began thinking about setting up a salt tank I purchaced a pail of this salt on sale using some of the credit I had acumulated selling cichlids. These credits are paying for my 20 gallon nano reef.
Since then I have seen references on line saying this salt is not very good (wether these come from people who have actually used it I don't Know)
The only issue I have seen and not a big problem as it is correctable is after mixing 17 hours the PH and calcium were a bit low.
A pail of this will last a long time with a 20 gallon tank and being basically a cheepskate I don't want to discard it without good reason.
I am a fan of Kent's reef crystals but they are the local boys around here. The cool thing about Red Sea salt is that it is actually salt made from evaporated ocean water, and not synthetic. I used it for a while but I prefer the synthetic stuff for keeping SPS corals I guess. I have less of a buffering and My attittude about water changes has changed over the years. (I do more.