Brown yellow spots.. need a diagnosis!

Hey everyone,
This is my first grow, and my plant was growing beautifully for the first 3.5 weeks, and now all of the sudden these ugly spots have shown up on my plant. I suspect nute burn, but my plants dont look like the other pics of nute burn that i have seen.
Could also be over watering, but i make sure the soil is bone dry at least 3 inches down before i water each time. The leaves on the bottom were the worst and i removed them, however it is beginning to spread upwards and i really want to correct it before it ruins it.
Here is my setup:
Strain: Jack Herrer
Age: 4 weeks today
Soil: Pure FFOF
Pot size: 2.5 gal
Small Growbox with ingoing and outgoing fans.
Lighting: 4x 26W CFL Bulbs
Nutes: FF Grow big, big bloom, (tiger bloom soon) Followed FF feeding schedule, how ever gave them half dose when I started for the first few waterings, I am now using a full dose every other watering.
Ph: unknown
Water: drinking water from wal mart

Attached are some pics that can hopefully give everyone a good idea of what im dealing with

THANKS!!

pics are a bit fuzzy but it looks like the lower foiliage (especially pic one top right corner) looks like a leaf miner. the other pics look like a mag deficiency problem. just my thoughts.

i think i figured it out. i thinks its just nut burns because i made a nube mistake and mixed my nutes in the gallon of distilled water prior to using them.. so i had nutes at the bottom of the jug that were like 6 days old.. i flushed it pretty good so we'll see if that helps..

[No pH information included] + [Funky leaves with lots of problems and spotting] = [pH damage]

I very much doubt it is a result of your solution settling. Given that you are using distilled water and no pH test... I cannot think of anything else more likely.

Get a pH probe for your water. They're $40 and worth EVERY penny.