leaves are turning brown (pics added)

the first is my power plant she is 21 days into veg she started of ok but now she has started turning browsn on the leaves i am using 600 hps light about 3 foot away from plants wass feeding a n b 3 times aweek but now stopped that to once a week not sure on temps as not got a thermo in there yet the second is a blue haze and she has only been in a week and the leaves are yellow on her too this is my first time so any helkp would be greatly appreciated
 

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