Help! Leaves are all turning pale yellow

I have three plants all ready to flower I inherited from a friend. Plants had mild spider mite/powder mold problem. They were all planted together in one pot filled with gravel. They were growing in a bathroom with a low wattage CFL. Plants were solid green if extremely stretched.

Last week I transplanted into three 3gal pots w miracle grow potting mixture soil and trained the stems to correct stretching. They were on an 18hr on cycle w a 400w mh light for a week until I turned it down to 14 three days ago. I sprayed w organic pesticide (fish oil, blech!) for mites/powder. I gave the plants one dose of foxfarm veg nutes. Watered every other day and once (when setting up my irrigation system) fully soaked and saturated the plants (probably too much water) and waited three days to water again after that.

Now plants are all rapidly turning pale yellow (looks white in pix) and leaves are falling off! Thought it might be magnesium deficiency so yesterday gave a dose of superthrive in a small amt of water (concerned big problem might be overwatering).

At first was fan leaves that turned yellow but now even new growth is yellowing (close up pic is of new growth). About to leave them on autopilot for a couple of weeks of vacation and trying to stop the problem before I have to go out of town.

Also spider mites are still hanging out and causing trouble. Any nuclear (I would do organic but at this point I just want the f*ckers dead) solutions to mites @ homedepot?

thanks!

Any ideas?!
See attached pix

Combination of MiracleGro and additional food is what it sounds like to me. Classic nuteburn IMO.

Yikes I've seen a lot of yellowing plants lately on here but these little ones are very yellow. I'm no expert by any means but here's what I'd do:

-Flush the plants to get any buildup/bad shit out of the soil, then start fresh with some PH'd water and nutes. As close to 20/20/20 as possible for now.
-Maybe give them a pinch of epsom salt per gallon w/ their water.
-Have their light cycle be on 1 of 3 settings and stick with it. 24/0, 18/6 or 12/12 when ready for flowering. (Get them healthy before flowering.)
-Put about an inch of perlite on top of the soil to helpkeep the bugs down.
-Home depot has some organic pesticide spray that works ok called Ecosmart that's based on natural oils like rosemary, tyme, peppermint etc. that you can hit the top of the soil with but don't put it on the leaves. Neem oil would be better for whole plant coverage.

Also how far away are your lights? I'd keep them at least 18 inches above them. Peace. =)

It looks to me like it's either a Potassium (K) deficiency or a Nitrogen (N) deficiency.

I would recommend putting the light back to 18hours and give them fertilizers high in K and N. Good luck, those things sure are sad looking.

as for mites, nukem with Hot Shot No Pest Strips. http://www.amazon.com/Hot-Shot-Products-Pest-Strip/dp/B003A2E394

at this stage of the game with a severe infestation, it certainly won't hurt.

then again, as sick and also spindly as those plants look, and the fact that you have a severe mite infestation and the fact that you are going on vacation, maybe you should just pull the plug on this grow and kill them. Clean out the grow room really well and use bleach everywhere. Hang the no pest strips and any other insecticed you can find and leave the room until you get back from vacation.