Wow that's a great question that has never occured to me because i've always used RO water.....and I must say I'm honestly not sure what would be the correct ratio imo. I'm really glad you asked that however because now I will go find out for you and then we'll be that much more in the know. With regular tap water you should not need your CalMAg at all but give a me a day or two to contact THE BRAIN (my hydro guy) and I'll find out for you about the correct ratios and whether or not you would use slightly lesser numbers for your base nutes.

When I turn my plants I actually do keep them on the grow nutes the very first week of bloom and then switch them over during the second week.....or perhaps even later if they've really taken a jump as they seem to do in the first couple weeks of blooming.