Mataro Blue Autoflower ~4 weeks, yellow spots and dying/limp fan leaves

I posted another thread in the newbie section a couple of days ago showing my plants which was concluded as just burn marks from water splashing on the bottom leaves during watering. I now am seeing more yellow spots developing on higher leaves, while some of the larger and smaller, but lower first set of leaves are wilting and limping down.

So far the setup consists of:
400w HPS
3Gal Smart bags with FF Happy Frog
Ph'd water at 6.5-.7
Temps mid 70s, rarely ever seeing higher than 80 degrees
18/6 light cycle
NO NUTES YET

I've heard that this strain isn't fully dialed in, so I'll have to switch to 12/12, which is maybe what these babies are asking for? Putting more effort towards bud site development and letting the lower foliage start to die off? Let me know what you think! I'm even throwing around the idea that my fan which was pretty dusty before I cleaned it off may be blowing something funky around?

Link to other thread here: https://www.rollitup.org/newbie-central/582442-21-days-into-mataro-blue.html

PICS!

I went and got the full line of FF nutes. On the back of big bloom it says 4 tablespoons for general feeding/gal. and heavy feeding is 1/2 cup per gal. Should I be using big bloom only at first or tiger bloom in conjunction at regular or heavy feeding (2-3tsp/gal regular, 4tsp/gal for heavy)? I will be ph'ing back to 6.5-.7 after adding nutes. Once I start the feeding, should I do as instructed per bottle - feed every other watering or do as I have read online: feed, feed, water?

Either way these puppies are being switched to flower tonight and we'll see the results! My first time messing with auto-flowers and so far the experience hasn't been so bad.

Should I trim off the dying/withering plants tonight before letting it sleep and hitting it with its first dose of big bloom? Possibly wait a week or two to use tiger after I see how the babes like the big bloom.

Thanks everyone here!!

Edit: where it says big bloom, I meant grow big like the above poster mentioned. However the plants are already over 15-18" so I figured I might as well start flowering. Maybe a couple of feelings with grow big and seein if that doesn't help with the leaves and spotting situation, then switch to flower.