I was using a 50/50 mix of regular instant ocean and oceanic. Recently switched over to reef crystals. If you switch, make sure you do it slowly not to shock your system. I started out mixing a small amount of reef crystals into my mix and slowly increased the amount until I ran out of the others. I did it over a 2 month period, but I don't think it's necessary to drag things out that long.
My tank is SPS dominant, with a high demand for alk/calcium/mag. So, I use Reef Crystals for their high numbers for those elements. Been using it for 3 years. If I had a FOWLR, I probably would use straight IO.