Dude that leaf could mean so many possible problems. Yes that leaf is deficient mag. probably cal too. Post more about your setup if you really want to identify your problem.
lots of times it's caused by root problems or wrong ph.
white leaf tips are a good indicator of a Magnesium deficiency.
A magnesium deficient plant is identified by intervenial chlorosis, necrosis, and eventually a lockout of plant nutrients. The problems starts at the bottom of the plants and works its way up.
Chlorophyll has the same structure as Hemoglobin, except that it has a magnesium atom in place of the Iron atom. Chlorophyll is how plants make sugars to feed the process of building ATP through the Krebs cycle.
Treating with an Epsom salts mix will clear this right up.
MAGNESIUM (Mg)
Lower leaves yellow and may even turn white while veins remain dark green. Blades die and curl upward.
I see no interveinal chlorosis. Brown spots are usually calcium related. I would be looking at your water...tap vs RO and whether there's any calmag in the mix.
JD