it definitely looks like a bit too much nitrogen. however, ive never used hydro, so im not sure how to fix it. maybe just drop the concentration/use pure water for a few days?
(no clue though)

also, 8" may be a bit close for 250w hps, depending on the bulb and its ventilation. do a heat check with your hand,since any heat stress would only aggravate other stresses.

once again, im not a hydro grower, so dont blindly listen to me until someone else can back it up