I have use RC a couple of time to start a tank, was not happy with it. Then I went back to my old reliable RS Coral Pro and was fine. Someone made the suggestion to try Aquaforest reef salt. I was a little apprehensions for the reason it is a pharmaceutical salt and the inconsistency of RC, but now running the Aquaforest salt was a good move. My tank looks better, and it mixes real fast. I mix the salt in a 5 gal bucket with a power head. Once the water covers the power head (1/3 full) I drop the salt in and by the time my bucket is full or RO/DI I am ready for a water change.
If you are doing a pre-mix the pro biotic only has a 24hr shelf live from what I have been told.