Leaves getting rust spots and then curling up and dying

http://www.growweedeasy.com/phosphorus-deficiency-cannabis
not sure but looks like that to me

the general practice when flushing is to pour at least 3 time as much water as the volume of the pot through it. do it slowly and let it dissolve the stuff in your soil as it goes.

ok thank you Roger, really appreciate the info.

Looks like heat stress to me, tips curling upward. Just did the same to one of mine a month back while playing around with a new 30amp heater that was placed poorly overnight. My gh temps never went over 70F, but I sure as shit had a hot spot that caused heat stress on one plant.