Help Me..... Yellowish Browny stuff

Hi Everyone, have got some Big Bangs and Big Buddha Cheeses in vegg and have started to get some Yellow brownish stuff on the fans leafs mainly and its really starting to freak me out.

I did hear that the Big Bangs like PH @ 5 - 5.5 and the Cheese likes 6 - 6.5 so not sure if it is this but let me know your thoughts here is a few pics -






Any help would be great people.

Thanks in advance

Could be PH but abit more info would help alot .
How old are your plants.
whats your nutes
Lighting .

Grils are 4.5 weeks old, lights are 2 x 400w HPS and nutes are Canna Vegg so far only about 10mls per 12ltrs. Only have had the second HPS light on for the last few days but have had this prob for the last 2 weeks. Keeps poppin up on one then start to notice it on another plant.

are they 4 weeks from seed or from cutting , Is the pics of the big bang or the cheese ???
If its the big bang then i would say youve been mis informed .
Ive only grew in soil and keep ph at 6.5 always no matter what strain .
Where is the damage , At the top of the plant or bottom

pics of the full plant would help

well PH has came from breeder themselfs and feeding sched and soil, only reason i cant speak to him now is that he on holiday for 3 weeks. (just my luck)
1 leaf is of the BB and 1 leaf is off the BBC. Danamge is on mainly bottom fan leafs but has worked its way up to the second set now,

Come on guys any tips or anyone got any thoughts to what i could be am really getting edgy now

check stickies plant porblem (check here first)

Yeah have done that but no pin point to what my prob is, Come on experts giver me som einfo