Adding Cal/Mag -Distilled water

Im using Fox farms OF/Light warrior 50/50 mix with some added perlite.
I plan on using distilled water, i hear its fine to use distilled water but that i need to add a cal/mag supplement. Im going to use jacks classic nutrients, just the bloom nutrient...the 10-30-20 or whatever it is since im only going to veg my plants for 2 weeks. I also have some Big bloom from fox farm. When would you think i need to start adding the cal/mag to my water? And how much? I could add some dolomite lime, yes i know, but fuck that.
My tap water is horrible and i dont feel comfortable using any water that I am unsure of what is in it

I use a teaspoon of calmag to a gallon of distilled or ro filtered water every time I water. I was giving them calmag every 2 to 3 times i watered but i kept having issues with mag def. Now they are showing a little N burn because the calmag also contains Nitrogen. I guess I need to back off on the veg ferts a bit. I'm going to try the lime next time.