You're growing in Hydro and you haven't checked PH?
That's what's wrong with your plants.
It's a magnesium deficiency for sure, but not because you don't have enough magnesium but because your PH is most likely jacked and Magnesium is locked out.
Check your PH and get it somewhere between 5.5 and 6.1
I agree. Unless you know exactly the formula of chemicals which will get the right pH and ppm for a certain amount of water, there's virtually no chance of being successful in hydro without pH and ppm/EC meters.