Yes and no ..... sorry I hit some Liberty Haze and I get chatty and nerdy when I do so bare with me lol
I always add calimagic (cal Mg and iron) to my RO n DH waters. I also add General hydroponics B Essentials (micro and submicro elements ) both at the recommended dose and never exceeding 350-400ppm ..... I do this just in case I am missing something due to the kind of water I use even though my base nutes (FloraNova BLOOM) contains plenty of calmag and other micros. Now, I also add those only when I change my res. And not to the topoff mix. I add little calimagic to the top off with the base nutes just because my girls eat lots of calmag. Try to read your girls. If your base nutes by itself in the ro or dh water show no sign of deficiency in the girls, why waste money on unnecessary additives. But if they show signs of calmag def, then that means the base nutes dont have enough of it and supplementing is a must.
Mixing little tap water with the dh may replace some of what youre missing (especially its buffering capacity) therefore somwtimes I add a cup or two to my mix for its buffering capacity to help stabelize my pH.
Now in terms of tap water having enough mg and cal .... well thats where it can be confusing a little. Apparently and based on a scientific paper I read, not all the cal and mg in tap water is absorbable by the plant. So even if the ppm is high and you know you have enough cal and mg, it doesnt mean the girls are utilizing all of it although theyre good to stabilize the pH. In this case paying attention to and reading your girls will let you know that the cal and mg in the tap PLUS whats in your base nute isnt enough ....
also the medium can have a factor in the cal and mg absorption. Coco grows tend to require supplimenting cal mg ..... i hope this helps and that I didnt confuse you.
Check out my current TriStrain grow:
https://www.rollitup.org/index.php?threads/883569/
