Kinda depends on how often you do water changes, what you keep in the non fowlr
tank as far as corals and how much of a water change you do. If you are keeping corals that are consuming the elements in the reef crystals then you dont want to mess with that, or you can do more frequent changes with the non reef crystals. i have 3 32g brute cans so i usually have one with reef crystals and one with regular I/O for my fowlr
tanks. I sometimes will use the reg i/o for the reef but not too often, maybe 1 out of 8 changes I will use the reg salt. But I feel ya on the price, its crazy how much cheaper the reg can be if you catch a sale. Its like 36$ on amazon last i checked.