I use General Organics CaMg+ and love it. I go with 2 tsp. per gallon to correct a deficiency, otherwise, 1 tsp. per gallon every second or third watering. Just read the plant, give her what she wants.
I use RO water also and have been supplementing cal/mag with molassas at 1tbsp per gallon . Ditching the mollasas though and going to use a liquid cal/mag sup .