I did contact Lou @ Tropic Marin USA and here is his response to min tank size and need for large skimmer.
"I can't think of any reason that there would be a minimum tank size for using Bio-ACTIF SYTEM Salt. In fact, I would think that it would almost make MORE sense to be used in a smaller nano environment."
"It is true that Bio-ACTIF SYSTEM salt is a little like bio pellets in that they are both forms of carbon dosing. It is also true that it is good to be running a protein skimmer when carbon dosing, but it does not have to be BIG! The volume of the tank has nothing to do with it."
In the end it all depends on your individual tank and needs. If you are already carbon dosing, then Bio-Actif could help you reduce your daily dosing. If you don't, than Pro Reef will work just fine.