Weird Yellowing Help

I have just had this problem show up in the last week since they started to form bud's
I have checked the guide's plus flushed my pots they are in.
Sorry the photos are from a webcam since i dont have a digi cam.
anyone got any idea's what it is as i am losted, thinking it might be 2 diff thing's but dont really want to mistake it with the wrong thing.
She is a SSH auto fem aswell

I am in soil pot's, ph with run off is good, plus hemid is sitting on %52 in the room, Last feed of nute's was wednesday 11th i have a few plants but its only on 2 of them :S

bro give me some better pics showing pots and all are you in veg or flower?more info and i will help you...

pots are 15 litre, being auto's, just coming into flowering now week 1 and since they are auto's they grow fast, I dont no anyone with a digi cam and thats the best my webcam can do, sorry for that, its on the top leaf's only starts from tip going back a weird yellow colour, stems are still the same no red in those yet, its a very bright yellow aswell, i have flushed 2 times over the past 3 day's, Hoping it might fix it, Nute's im using is budzilla NO1 used 5 ml's per litre of water once and 2 of my girls went like that 2 days later, so flushed after i seen it happening

using 600 watt hps lamb aswell temp's are good in that room, only 2 of the girls have started that, the rest are all good, used the same water which is rain water not tap water, same nute mix for all of them, so it has been wondering dont no how good the pic is as my webcam sucks

either magnesium deficiency or potassium deficiency

i was thinking mag or potass, so i have flushed twice now, when should i start back on nute's? and it has slowed the growth aswell of that plant in the head forming, forgot to add that in, any quick fixes for this as it is one of the better plants with the node's

start your nutes at a reduced strength right after the flush

Cheer's for that dillest, I will put some lime in 1st to see if it is a mag problem as i dont want to miss it up and potash in the other one since its only 2 of the girls showing it, thanks for your help man means alot for a new grower