Please help my little girls!!

So this is my first grow, and my setup is as such. I've got 8 plants growing from seed and they're a little over a month into veg. I've got them under a 600W cool tube MH inside of a 4'wx1.5'dx6.5'h white particle board cabinet. Light is kept between 14" and 20" from plant tops. I transplanted them from solo cups into 2.5 gallon buckets about 3 weeks ago. Soil is composed of roughly 2parts foxfarm ocean forest, 2 parts miracle grow potting soil, and 2 parts perlite. Drainage seems to be good, and the plants have responded well to the transplant. I'm watering them thoroughly every 6-7 days...completely soaking the soil and then waiting until it's pretty dry about 3 inches down (finger test) to re-water. Temperature is well controlled and the cab. stays between 70 and 80. I was originally using a window a/c unit to duct in cool air, but now that the weather is cooler, temp is kept stable by pulling air out through a filter and a 290 cfm squirrel cage. Pic will be attached. Recently some of the leaves have started to look sick...yellow and brown patches, brittle, etc. Otherwise they seem to be very health. I can't narrow the culprit down between mosaic virus, thrips, or a deficiency of some sort (total newbie). Please let me know what this is and what to do. Many thanks in advance.

What kind of water are you useing?

You looks to be on the right track.
TMV looks possible.
Thrips also could be.

I would use a NPS(no pest strips) to eliminate one option

I've been using water straight out of the tap...public water, haven't checked, but I don't think it's either too hard or soft, and the problem seems to be isolated on two plants. I've been looking and haven't found any little critters. Humidity may be a problem as it's usually around 56%...any chance this is a deficiency? Is there anything that can be done to reverse TMV?...should I remove the affected plants?

As long as you live in the US your tap water "should" be fine. 50%+ Humidity is fine.. not good but fine.

I dont have any exp with TMV outside of the signs.

pic 3 looks like a Leaf that should still be on the plant, and mag deficient

It's because you need to put it into some new FFOF soil. IMHO if you're mixing your FFOF with other soils, you should already be supplementing with some liquid nutes. Just my opinion. I know when my plants start looking like that I have to transplant to fresh FFOF and they take off like no tomorrow.

it is a boron deficiency...to high of PH or over ferting will cause this...foliar spray with lights off of course some boric acid...1/2 tsp. per gallon ( boric acid = eye wash )

i have to say though, my girls get it almost everydamn time...badly too, but it never seems to effect the yeild to much, and normally starts at like week 3 or 4 of flower. i to use ffof, and i have to say...next go i am switching to some pro mix, and light warrior mix...heard its good shit.