Grow Mediums Calmag ec question

[Fisherboy]

Hi guys,
Anyone give me any advice please as I'm scratching my head a bit. I grow in coco with LED and have always supplemented my feed with calmag. An associate I was talking to yesterday said he adds his calmag to his tap water then takes an ec reading. He deducts this total from his total ec after nutes to get his nutrient ec and tops up the nutes to get the desired ec as per the manufactures feeding schedule.
I've always included my calmag ec in with my nutes and not my tap water. His reasoning was that the calmag was almost impossible to burn plants with so takes it out of the equation.
Anyone else out there deduct before?

 

[jingoba]

There way you're friend does it makes sense if he's afraid his total EC will be to high from time to time and he needs to keep cal/mag up, as it's often the case with coco and LEDs.

I use reverse osmosis water so it's good enough to me to add everything in their correct order and then make sure my total EC is OK.