Helping out an ailing yellowing plant in autopot with MegaCrop

[terp182]

Problem: Two pots of three connected to the same reservoir are showing yellowing leaves, one more than the other. The Sweet n Smelly is yellowing on top, with signs of dried tips on some leaves. It appears to be spreading.
-Medium/grow method: soil; Roots Organic/Perlite. Autopots
-Feed and supplements used: MegaCrop @ ~500 ppm, BE at -1.1g/gal or ~75 PPM
-Water source: dechlorinated tap, 22 ppm base
-Strain and age -
1. Sweet n Smelly, 69 days, a week behind the others (had a long veg period) and is doing the worst
2. 3BOG - doing better and about ready to chop, but lots of lighter green/yellow in the leaves.
3. Sour Stomper - Thriving and riotous. Should harvest in a week or so.

-Climate: night and day ambient T and RH%; res' temperatures - 84 F/48 RH day, 79 F/60 RH dark (4 hours)
- Light used: 2xMarsHydro @ 24 inches, 75%
-Additional info: How long have the plants been affected? - on and off, the past few weeks. Recharge seemed to temporarily improve the yellowed leaves but for just a day or two.
--Pics below.
- My guesses: the Sweet n Smelly has an immobile nutrient def, indicated by the yellowing (and brown splotches at the tips of some leaves) of many top leaves. What to do about it, and how to address it without throwing off the Sour Stomper and 3BOG is what I don’t know.
Anyone have a thought as to how I can get these girls a little happier?

 

[Mañ'O'Green]

They look pretty good! I think you are feeding on the high edge of what autos need. Your RH is a bit low during the day for 84°F. lower the temp to 80°F or raise the RH to 60%


I run 18/6.

 

[terp182]

Oh man. I get to turn off the dehumidifier?
Cheers!

 

[Mañ'O'Green]

Oh man. I get to turn off the dehumidifier?
Cheers!

You better read that again. I will rephrase.

At 84°F you want the RH to be 58% to 62%

If you cannot raise the humidity then try lowering the temperature to 80°F in the day with 50% RH.

Try to get it in the yellow area of the VPD chart. It is for late flower.

 

[terp182]

Haha that sounded more flip than I meant it.

I’m watching VPD, just using leaf temp with my infrared thermometer. Riding the edge of the late flower zone.

Edit: dang the VPD calculator broke on the link I always use. Using the rough chart they have I’m good now - 80 degrees and 45-50%. I appreciate the clarification!

VPD link: https://www.dimluxlighting.com/knowledge/blog/vapor-pressure-deficit-the-ultimate-guide-to-vpd/

 

[low_and_slow]

With bottom watering setups like autopots, you're likely to get something built up in excess in the soil by the end of a grow because there's no way to clear out excess nutrients that the plant isn't using. If that were my setup, I'd just power through and maybe back off the ppm a bit, but a little yellow that late in flower won't shut down the grow. You could also top-water them until you see runoff, then put them back in the autopots, but that's probably more hassle than it's worth in the long run.

 

[terp182]

Thanks! I dialed in the VPD and will leave the ppm around 500. I appreciate the feedback!