I've been using Tropic Marin and last time I mixed some saltwater I used Reef Crystals. With Tropic Marin I seemed to always get this film on my mixing container and on my PH and heater, but it never transfered to my DT. This first batch of Reef Crystals didn't have a film at all, my calcium level was also a little higher, 420, which I like. So I think I'm going to keep using Reef Crystals.