do you have pics? also sounds like nute burn, what is the ph of water and nutes in and what is the ph of the run off? if they are differant than 6.0 then that might be the problem, also what is the strain, if it is a auto flower then 4 weeks of veg and 4 weeks of bloom it might be natual for leafs to do this, it would be at the end of its life, the only next thing would be having some balls drop to final polinate.