Dosing Calcium/Magnesium with RO

High Guys
Just got my hands an this dry fertilizer
Npk 4 18 38
This one does not contain any Calcium or Magnesium
I want to increase my Potassium(starting from bloom day 40) and chose this fertilizer to do so
Because I use RO water and the fertilizer has none I def have to add Calmg
I have calciumnitrat and Magnesiumsulfat.
Can you tell me how much to add?
I have stock solutions and power
Hope you can help me
Maybe reaching EC 0.3 starting from 0.0 and then the fertilizer till EC 1.5 is reached?
Hope you can help me
Beat wishes!

0.56g per liter calcium and 0.256g mg thats the offial masterblend recepie
Also 0.56g mastetblend basic nutrient
Thats what i use in hydro but each plant different needs bla bla bla

1 ml calmag/gallon
1 gram mag/gallon

I use the 15.5-0-0 with the Master Blend, so no need in adding Cal/Mag. 15.5-0-0 is loaded, with Calcium. I use Epsom Salts, for Mg, and Sulfur.
How much Mg, depends on stage of growth. My medium is Promix BX. I use less than recommended, and feed, with each watering. I habd water.

gr865 said:

1 ml calmag/gallon
1 gram mag/gallon

Click to expand...

But the amount of Calmg needed depends on the concentration of the product right?
The ones available for me are Canna Mono which is 14% Calcium and 7% Magnesium.
Going with 1ml/Gal seems quit a lot for me.
Which product do you use?

Ahh and one import info.
I am growing hydroponics

Why not use epson salt?

I would probably suggest that depends on the strain you are going to grow and climate....might need to adjust