Isolated necrosis on sativa

Underside of leaf.


Top of leaf.


Closeup of necrosis.


This has got me stumped because it doesn't appear to be systemic. This issue is only apparent on several mid-plant leaves on different stems. The rest of the plant looks very healthy. There is no pest problem. Guesses are welcome but I'm hoping someone has BTDT.

This is a pure Thai sativa that is grown in hydro using only Flying Skull dry nutes, Flora Extract, and Z7, plus Mendocino nitrogen-free Cal-Mag. Growing conditions are controlled and monitored electronically within very specific tolerances.
One month into flower.
pH: stable at 5.7
res temp: 68F day to 66F night
Temps: 84F day to 69F night
Rh: 70% day to 45% night
CO2: 700ppm to 1000ppm
Nute strength: 1100ppm Hanna; 900ppm nute, 200ppm cal-mag
PAR: uniform at 950μmol

Ph 5.7 all the time will lockout calmag. Even if there's heaps there.
Calcium excess will usually start as brown spotting from the veins. Then spread outwards.
Calcium deficiency, the spots are more sporadic. That's what it looks like you have to me.
You're supplementing calmag. So it can't be, that there is none.
IMHO.
Try letting your reservoir / medium / runoff rise, to just over 6ph, before you top off.
I do believe it's your ph locking out calcium. It's quite likely a calcium hungry strain.

Thanks, Tim, I'll give that a try and report back in a few days.

Rider509 said:

Thanks, Tim, I'll give that a try and report back in a few days.

Click to expand...

No worries.
Good luck.