This why yo need a pic or two. Ya the rock wool has too dry out depending on how big
is yo rock wool. I seen it where it don't dry out around the main stem and it just rots
right around the stem. If the rock wool is bigger yo git root rot if it don't dry out~
yo leaves drooping too from...
Yo wat up? Ain't nutting rong leaves look good?
How high is yo 600 watter above the plants?
Yo u talking bout that new growth that's really yelllow?
That's from a good feeding of nutes, did you just give'em
a good dose of nutes? Next watering just given plain water
a regular watering no...
Do yo check the ph and ppms of yo waterings?
A half ml/l of bio bzz or whatever yo feeding
is like Chinese arithmetic to me~ How many
ppms is it? I'm agree it's not looking like nute
burn but possible under feeding or the feeding
of the wrong type of nutes all together.