Need help with my plants, new growth slown down, curling top leafes and yellowing

Hi folks,
i need some help for my babies! For a week or so i noticed that growth has slown down and the top leafes are all curled up with the tips on some of them starting to yellow.
About the plants: grown from clone cheese strain, i placed the rockwool cube straight i nthe pot, and they have grown very well for the first 3 weeks, i use 4 cfl 6400k 30w and 2 days ago` i added a 23w 2700k as side light.
I used miracle grow soil and watered them with tap water left to rest 2 3 days, every other feed i gave them a 1/2 strenght miracle grow fert.
Few days ago` when i noticed that growth was slow and the top was all curled up, i gave them a full dose of miracle grow fert including misting the leafes, i gave it in total 500ml of water.
I feed my plants every 4 5 days.
Yesterday asking advice i was advised to flush the plants which i did, also the suggestion of air movement, i already had a pc fan in my grow space (1.5ft x 3ft) however i left all last night and today all day the door of my grow space about an inch open and placed the fan right by the door wo that the air from the room would be brought in.
However tonight still not improvement, as per i was planning to start flowering next week, can somebody advice what the cause might be? and if i need not to worry too much and start the flowering? or are my plants going to die?
I enclose pictures for your viewing.
Tanks in advance

cut back on the watering some,and they should bounce right back,no real problems from what I can see.

First off...i've had some bad results with MG soil...there's time released fert in the soil...so whenever you water, you're releasing more fert into the soil...so you never know how much fert is going into the soil...on top of your nute feeding.

MG potting soil compacts too easily and doesnt allow great aeration...try to transplant into a beneficial medium...so 1/2 perlite and 1/2 vermiculite...you can do this by removing the existing rootball and washing the soil out of the root system with tepid H2o...then fill 1/2 a pot of vermiculite/perlite mix...put roots into the mixture and fill up the remaining pot full of 1/2 1/2 mix...and then water with transplanting mixture...give her a coupla weeks of revival and regrowth before hitting with full strength nute schedule...

Yeah,I'm dead against growing mj in MG soil because it causes nutrient pockets,hot spots,etc..Try as we might,we just cant seem to convince people to get some good soil.

eh, well, i'm just as guilty for using it in the past...but thats the past...at least i can give my opinion on MG soil based on experience...not just knocking MG soil for the sake of it...

me too.Grew 1 in MG Organic Choice,1 in MG Moisture Control,both were all f'd up with nute probs,but did grow.

same here. my brother told me to stay away from it but i didn't listen... 4 weeks into flowering it fucked me hard... Spend the extra couple bucks on the FFOF soil or another good soil and you won't be dissapointed