Cal Mag

Hi all new to hydroponics so here is one of many of my stupid questions. Do you use Cal Mag in hydroponics, if so when would you?

It is needed when you use RO water. Tap water might gave all that you need.

I use tap water and still put in cal mag as I've had issues before

It is used with RO, Distilled, or other water sources low in ppm and lacking certain minerals. It restores the water with these Minerals(Cal., Mag., and Iron mostly) at the right ratios.

Calmag is also need when using LED lights.