nute burn? P deficiency???

I've studied all the pictures and can't figure out if this is nute burn, phosphorus deficiency, or something else. Plants are in soil, 3rd week of flowering, under 600 hps, about 1.5 feet tall, fertilizing with PureBlend Pro every other watering in the amount suggested for mature plants. The tips on some of the fan leaves are turning brittle and falling off, other leaves are turning brown on the edges. The plants look pretty healthy otherwise. I don't want to fertilize if it's nute burn, and I don't want to flush if it's underfertilizing. Help please.... Pics are attached.

wont hurt to give it a good flush. always helped any of my problems. i say back off on the nute strength after u flush the shit out of that soil

i agree nute burn turns the edges brown like that first then sets in the rest of leaf. flush and lower nutes. btw what's your ppm/ph readings?

This may sound stupid but whats the method of flushing?

run atleast double amount of plain ph'd water than soil. say u have 5gal buckets. run at least 10gal plain ph'd water through the soil