How often should I use cal-mag if I’m using RO water ?

Hi, just wondering how much cal-mag I need to use and how often with RO water. I’m using fox farm grow big and my plants are about a month old

I use a TBLSP per 5 gallons water, and use at each watering/Feeding. Slightly more in weeks 5-6 in an 8 weeks flowering strain.

Though I use Epsom Salts, and use 15.5-0-0 for calcium.

But Id use a small amount each watering. Those nutrients are quickly used, and weed is a heavy user of Cal/Mag. Others will chime in.

Always add 5ml/gal of cal mag when using RO or distilled h2o. You are replacing minerals that are normally in the water.