leaf rusting????

HELP!!! a few of my larger fan leafs have started to develope a rust like look and are now drying up and crisping, ther ein ther 5-6th week of flowering and the buds look great about 10% of the pistols are turning brown but im worried bout these leafs effecting the whole plant, i have spidermite that im having an endless battle with and ive use a pk power from wilkos in the soil. please help me

sounds like nute burn,got any pics?

lock out causing a cal mag deficency. Ph your water to around 6.3 on your next watering.

im trying to get some pics up but my g/f dont like me taking pics on the family camera!! ok cool, lock out was what i was thinking im going to use just water for the next few days then get the ph level back. any ideas for the spider mites ive never had them before but this time round i used clones of a mate and he has the little fuckers too.