Yellow tips on fans

Hey, Im currently on my first grow, its a tent grow in an ebb & flow system on fox farm nutes currently under a t5 fluorescent. Ive been getting yellow tips on the top leaves and some of the bushy leaves close to the stock. Plants look great and have looked great for the 2 weeks they have been in veg. I use tap water for my res if that matters and so I kinda figure that might be what it could be but these are the first leaves to the yellow so far. Any Ideas?

Hi my plants on week 5 of flowering and i have had yellow tips on my leaves on and off. i think it has something to do with how you mi the nutes i got mine the last time when i added boost. Im growing under a 600w hps in an 205 nft setup i use tap water too.
The first pic is my first grow thats nute burn the second is my current hydro grow