Brown/Black Leaf Edges / Dieing Off?

So I'm not quite sure what is going on here.

RDWC
PH 6.0 (to 6.3 over the week)
PPM 800
Water Temp 70F/21C

RH 50%
Temp High 22 / Low 17

GH Silica-CalMag-Micro-Grow-Bloom. (Plus the rest of the line at half strength or less, Any of the GH organics products I mix in with the Heisenberg Tea I feed them twice a week).

It's pretty much only the really bottom leaves/ leaves sort of tucked in not getting a lot of air? (Despite the aggressive lower canopy lollipopping I did earlier.)

Side Note: [I had put two cuttings into soil so I wouldn't have to water too often (compared to hempy). I think that soil had Fungus Gnats! (I set some yellow traps which seemed to help control the issue. Haven't seen too many really. Need to do a Hydrogen Peroxide water next. But Not sure if that is even related to this?]

Phosphorus deficiency. Do you have a meter for EC/PPM? If not why not with hydro?

PPM is ~800 (750 with base nutes, then goes up to 810 to 830 with the heisenburg tea and rest of GH line)

That's what I was guessing but the other factors were throwing me off. I already feel like 800 is fairly high no?

OH! OH! I jut realized something haha. Makes sense. I'm feeding transition feeding 5-5-5ml m-g-b. Today's water change day, and transition period is over, they go to 5-2-10 m-g-b-.... that should help with the P deficiency!

Sometimes I just need to talk it over with another mate. Thanks @hotrodharley !