Somebody please help my plant is dying before my eyes!

What would cause my PH to go from 6.4 going in down to 4.9 in the runoff? Soil is Roots Organic. It's causing severe nutrient lock out. 5 other plants are fine.

the medium is most likely the problem raise your ph to 7 going in. also if you measure ph before adding nutes it will change when you do add nutes. check this constantly as you adjust your routine. what roots formula are you using? they have a number thing going and each one is different. looking at those whispy leaves is not promising.

At this point I'm not adding nutes - essentially just flushing with 6.8PH water in a drastic effort to get the run-off PH up. I'm 2 gallons in and still getting 4.9. Dolomite Lime? As far as medium it's Roots Organic Original in a 5gal. Thanks for the help.