Yeah, you'll need the full 10ml per gallon throughout. You could get away with 5ml per gallon in veg but not in flower.

Tap water is not a substitute for CalMg. It could have a million ppms and none of it from Cal or Mg. If you had a city analysis telling you what the ppm of Cal and Mg where in your water then you could tell if you need it or not. Thats why we RO the water down to a clean canvas and simply add exactly what our plants grow best on.