One big difference in Reef Crystals to Instant Ocean, both made at the same plant, is the Reef Crystals contains both vitamins and a metal chelator. Instant Ocean has neither of these. The issue with brown scum seems to happen when the mixed water sits for a week or more, it allows those organics to drop out of solution making the brown gunk. The metal chelator might also contribute to the problem. So I guess the trick might be use it soon after its mixed and settled. Like maybe 24-48 hours. That might be the difference, I don't leave saltwater in my barrel, I mix it up 24 hours before I use it.