Please help! Urgent! Nute Question

https://www.rollitup.org/hydroponics-aeroponics/143816-how-do-you-add-nutes.html

refer to that link please! it has my question and my plants are turning VERY yellow and not doing good because I don't know WHEN or HOW exactly to add my nutrients.
TY.

unless i misunderstood, Thats probably another defieciency, i've had it before, you need to get some Epsom salt from your local drug store like Boots, or if you are in the U.S.A wallgreens?

Its is a magnesium deficiency