Plants Leaves Are White On Edges

First off im using hydroponics,my ph is 6.5
all signs are go,my fan leaves are growing huge but just last week the new leaves coming out the top are stunted,uneven,and whitish yellow forming around the edges,it look like they are deteriorating.
Can anyone please shoot some ideas,its my first hydro grow.


I have a 400w HPS light
constant cool fresh air coming into room
room is 80F
water is 22c
Light is 18inches from plant
nutrients are mixed correct
no signs of bugs at all


what is wrong?

There might be a nutrient deficiency

it sounds like some type of nutrient deficiency in my limited experience with hydro. how often do you totally change the res? also how do the roots look? how old are the plants