This is the only plant out of 8 to be doing this. Strain is Purple Wreck. Cool tube with 600W MH is 15 inches away. I took a couple gallons of water out the res and added some distilled water back into it (to lower the ppm). I was at about 715 ppm using a 0.5 tds meter. I brought it back down to 600 (because it was doing well there since january 2nd). This problem arose like 3 days ago and has very slowly progressed. Been keeping PH at a steady 5.7-5.9 and not letting it fluctuate much. I've used PH Down almost daily and Ph Up once or twice. I saw a salt build up on the side of the res like 2 weeks ago. It was before it needed to be topped off with a few gallons so I just topped it off in hopes of dilution. It's been fine for all that time until the last 2 or 3 days. The stems are kind of purplish (which I heard can be normal or sometimes can't be... great ) It's mostly on the lower leaves. Very mild on the upper leaves.