HELP!!! small yellow/brown spots on bottem leaves

Hello all, basicly these yellow spots started to appear on the first proper leaves (not the nute pockets).
The spots are starting to appear on the next set of leaves up at the ends of the leaf also.

Specification:
Size tent - 110cm x 65cm x 160cm
Light - 400w duel spec (currenlty 18-6 hrs)
soil - Biozbizz Light mix
Nutrients - Ionic Grow for now
Strain - Lemon something? FROM SEED (bagseed)

Temps around 22-27*C
Humidity around 30-40%
Soil ph - 6.8
size - 5 inches tall
distance from light - 18 inches

week 2 - fed them 1.5ml ionic grow mixed into 500ml volvic water ph 6.5 on there 2nd week due to the soil being a "light mix" misted leaves with water.

week 3 - fed them 3ml ionic grow mixed into 750ml volvic water ph 6.5 on 3rd week. misted leaves with water every other day.

My question is ... what is this problem and what can i do to fix it? CHEERS!

I use bio bizz light mix and their nute range,

I would say the spots are from misting with the lights on causing the droplets to become microscopes and burning the leaves.

I've never done foliage spraying, also the light mix is good medium if you have good nutes, I can't comment on your nutes as I've not used them, leave it be with no spraying and if the new leafs develope the spots then look into deficiencies, but for now chill out and give it 10 days, most strains bounce back on their own within 2 weeks.

Good luck mate

EDIT*** Also stop using bottled water, I did to begin with but has issues, since changing to tap water I've been fine and I've never checked my ph in 7 years of gardening

If those spots are actually yellow, (kinda hard to get a read on true color in your pics) then a shot of Ca and Mg would do ya, but if they are rust colored, then it is most likely a P deficiency.
I also think I saw some nute burned leaf tips in pic #3.
*you can quit misting them, they are big enough to take up any moisture they need through the roots.

Since ive noticed the spots i stopped misting them with water as i thought this was the cause. I notice there starting to form on the next set of leaves up and that makes me think its not the misting that was causing the problem. ive tryed to narrow it down to a specific def but i just cant find a picture with any resemblance to mine.

The dots start of very small (1mm 2mm) with a yellow colour and gradualy get a little bigger (2mm - 3mm) turning light brown and looks as if its burnt or dieing on the spots. any ideas??

what is Ca and mm? .. i know its got calcium and magnisim in but is it something i add to the feeding scedual or a one of dose?

any info is gold dust to me thankyou !!