MAGNESIUM (MG) Deficiency
Magnesium is a mobile element,Magnesium deficiency usually starts in the middle of the plant and spreads to the younger leaves. Leaves turning yellow, or even white, with the veins remaining dark green is the best indicator of Mag deficiency.
Magnesium can be easily absorbed by plants when the PH range of is 5.0-7.0 ,also other factors may reduce or lock-out the mag uptake, such as a permanent humidity, low temperatures, or acid and cold substrates.
As Calcium,magnesium deficiency usually appear together,so usually get Cal-Mag supplement
First adjust the PH level:
In soil, magnesium is best absorbed by the roots in the 6.0 - 7.0
In hydro, magnesium is best absorbed by the roots in the 6.0 - 6.5 pH range
Adding more magnesium to your growing system,but not overdose,otherwise will also got trouble.
Flush your system with clean, pH'd water that contains a regular dose of plants-friendly nutrients that includes magnesium. Such as:spray with a 2 percent Epsom salt.