Hey Blazin...red stems are usually P deficiency, cold exposure, or genetics. if there is Mg deficiency the first thing that will happen is the leaf will curl up like a taco.
Perhaps I should qualify myself, red stems and yellowing can be related to deficiency of both N and P, as well as Mg. However Mg usually appears as taco leaves first.
Mg deficiency usually presents as upturned serrated edges on the leaf (as if they're praying for Mg). To much Ca, Cl, or N from NH4 sources as well as pH imbalance can lock up Mg. Too much Mg can lock up P. Middleagecrazy must have memory loss - the dilution for epsom salts (MgSO4) is 2 tablespoons per gal H2O.
Peace
the stems for the leafs are red is this a prob?