You'd only need about 2 tsp 2x a week of Epsom salt and maybe the same for Ca.

I really doubt your plants need more than that, and that assumes you are getting little from the tap as well.

Unless you are using 75 GAL of RO each week to do water changes........not likely.
Even there, blending with the tap to get a decent GH is wise.
Higher GH's are fine etc, but they are not needed.
All you do is add enough to rule out a limiting nutrient.

Regards,
Tom Barr