Severe Root Burn

[qze]

I have had my lc in Prime-Agra for about a year now and fertilized it with MSU (pure water) at 100 ppm twice a month. In the past few months, it hasn't been able to put out new roots without the tips turning black and shriveling up, which is evident from the visible shiny salt build-up at the surface of the pellets and brown residue at sides of the pot. I read in another thread that the salts were alkaline, so I tried soaking the plant in distilled water mixed with vinegar and lemon juice everyday for a few hours. But that didn't make a significant difference. Is there any way to purge the salt from the pellets and the pot?