what is wrong with my plant

This is a strawberry kush clone that i had got from a freind aprox. 2 1/2 maybe 3 months ago i grew it the same strain before and didnt have a problem. i have been watering it with just water that i put in a 5gal bucket with a air stone, i tryed using nutes but it just got wosrt i dont no what is wrong i am thinking about cutting it down and just taking the loss. the leaf problem just keeps spreding thats why the plant is so bare because i cut the leafs off...... It is in a 3 gal. pot using foxfarm soil and a 250 watt mh all my temps are good i have other plants that are just fine its just this 1

Nute burn, flush the soil with PH'd 6.5 water.

magnesium def. epsom salts

I tend to agree with Buds, but QUIT PULLING LEAVES OFF!!!
Flush it, and just use plain PH'ed water for the next several waterings. NO nutes.
The burned leaves will not heal, but they still serve some purpose to the plant. When the plant cannot get anything more from them, they will FALL OFF.