Week 3 veg rust spots (pics)

hey
Iv just started my 3rd week of veg and i have 12 plants under a 600 w air cooled hood.Temperature is 75-80 humidity 60-65.1 of my blue cheeses has got really bad rust spots on the lower leaves.There is a tiny amount of these spots (barely noticeable) on a couple of the other plants and the rest are perfect.I have them in biobizz light mix and have been feeding half ml/l of bio grow for a week.Also have been feeding bio heaven once a week.
I dont think its nute burn caus its not attacking the outside of the leaves.I was going to up the dose to 1 ml/l today.
Do you think this will be ok? what do you think i should do to stop these rust spots spreading?

Do yo check the ph and ppms of yo waterings?
A half ml/l of bio bzz or whatever yo feeding
is like Chinese arithmetic to me~ How many
ppms is it? I'm agree it's not looking like nute
burn but possible under feeding or the feeding
of the wrong type of nutes all together.

get your ph in check n it should go away,kind of looks like a phosphorus difiency mayby a mg def.,you probably have lockout from ph being off,i just bought a ph tester for $6 from a fish store,not super accurate but you can get an idea,get a better 1 if you can tho

my ph is 6.5.i check my soil and feed with digital testers

don't be an idiot like myself, and calibrate your ph tester if its necessary. I have similar rust spots on lower leaves like that, and when I tested the ph the old fashioned way, realized the ph was at 4-4.5. Digital was WAY off. If your ph is at the proper level, and HAS been, then you may have a fungal issue, and want to lower the humidity to around 50%, and spray the plant with OH water laced with Neem Oil. Mix: 1 quart oh water, 1/2 TBS neem oil, 1/4 tsp dish soap, and shake that baby up and spray on the upper and lower leaves. Check in 7-14 days, and spray again if needed. Neem Oil is an all natural extract from the Neem Tree that is hell on just about any pest or bacterial or fungal infections.