whats wrong with this leaf?

using gh 3 part in dwc..and it is about 5 weeks into flower..i tried the lucas formula but went back to using all 3 parts as ive had very good luck with it in the past

as you can see not only are the tips burnt but so are the edges..the ppm is low..about 7-800 and the ph is perfect

It looks like either P or K deficiency. There would need to be whole plant pics or pics of the leaf in a later stage of the problem to say for certain.

thanks man...ill take some more pics tomm night and post em up