I'm using an MRC CR4 on a larger system (will be a combined 125, 120, 22, and 40B with 150, 100 and 50gal Rubbermaid tubs for filtration, etc.). I've had minor issues with it, but that can likely be attributed to it being my first Ca Rx. I'm bad about holding scheduled on dosing two (or three) part, too, so the reactor seemed like the best route. Getting them set initially is the fun part, then it is more maint checks to make sure it is still putting out enough/not too much based on growth and newer additions.