Thrips, Powdery Mildew, Nute Related? Not Quite Sure What To Think

Please Help Identify!!  (Look at pic's & Summary to shorten up) -Is It powdery mildew or maybe nutes got splashed onto those leaves or some type of pest?
 
I've got a problem I am having a hard time identifying.  I would assume powder mildew, but the highest humidity has gotten is 48% for approx. 15 minutes.  It stays right around 25-30% on average, occasionally jumping to 40-45% at canopy level for no more than 30 minutes at a time. 
 
The white powder sort of looks like sugar dusted in certain areas and can be scraped off.
Another interesting thing I've noticed is that it is only visible in the grow room under the MH.. If I cut leaves off and look at them under household light, it is not really visible.  Maybe this is because the MH is a much stronger, brighter light?
 
A weird thing; I have only noticed it on the healthier middle-upper fan leaves that receive plenty of light.  As opposed to the Nute-Defficient ones on the lower canopy receiving little to no direct light due to all the fan leaves/dense internodes.
 
So due to humidity/lighting I wouldn't think so.. Maybe thrips?  I have been preventatively spraying with a neem oil/SM90 Combo once/week (Went two weeks in between sprays once) and keeping the room clean.  They have been deficient most of their lives in either N or P b/c I listened to grow store owner and only watered w/o nutes at first.. Changed that up now. I haven't seen insects yet..
 
[SIZE=13pt]They are about two months old and the PH of infected plants = 6.6 and 6.5.  I have two oscillating fans, an intake/exhaust fan bringing in new air constantly, a dehumidifier, and have had the lights on 24/7 their whole lives (600W MH)[/SIZE]
 
[SIZE=13pt]Overall they seem healthy except for the nute defficiencys and this white powder which is very minimal ATM.  They are very vigorous.[/SIZE]
 
 
To Sum Up/Shorten:
[SIZE=13pt]Humidity Average:25-30%[/SIZE]
[SIZE=13pt]Humidity Highest Ever: 48% for no more than 15 minutes[/SIZE]
[SIZE=13pt]Lights: 600W MH on 24/7[/SIZE]
[SIZE=13pt]Neem Oil + SM90: Preventatively sprayed weekly, occasionally bi-weekly[/SIZE]
[SIZE=13pt]Temp: 72-75 degrees F.  Highest ever recorded: 80  Lowest: 68[/SIZE]
[SIZE=13pt]NOTE: Only on the healthier mid-upper leaves as opposed to the nute-defficient lower leaves[/SIZE]
[SIZE=13pt]NOTE#2-Have seen no pest so far[/SIZE]
[SIZE=13pt]Overall: They seem healthy except for the nute defficiencys and this white powder which is very minimal ATM.  They are very vigorous.[/SIZE]