Rust spots, yellowing

[Moose8810]

Problem:
Yellowing and rust spots, mostly on mid/upper leaves

Medium/grow method: Botanicare Coco/perlite 70/30 mix, 5 gal fabric pots.

Feed: and supplements used: Botanicare CalMag+ 2mL/gal, Growth Technology Ionic Bloom 8mL/gal, Buddha's Tree PK9/18 0.5mL/gal (tried a little more a week or so ago and got tip burn), Buddha's Tree Advanced Metaboost 2mL/gal which all ends up around 1.2-1.4EC, pH'd to 5.7-5.9.

Recharge used once or twice a week.

water source: Well water, 140ish ppm 6.8-7.0pH from the tap

Strain/age: Grower's Choice Seeds Gorilla Glue Auto, day 56 from sprout.

light used: 630w CMH (1x 3100K and 1x 4200K bulbs), 4x 3500K Autocobs, 2x 2700K Autocobs (5x5 tent, CMH in middle with Autocobs along the sides)

Climate: Lights on: leaf surface temp 70-72F (75-79F ambient), ~50% RH. Lights off: mid 60s leaf surface temp (~72F ambient), 55-60% RH. Dehumidifier is on constant operation and the tent is fully ventilated, not much more I can do humidity wise unfortunately.

Additional info: Two other GG's adjacent to this on the same feed schedule seem to be fine, but they also both stopped vertical growth ~5 days after this one with issues. One of them is just starting to show rust spots on 3 leaves. I always water to a good amount of runoff, ppm and pH of which is in line with their feed.

I'm not sure which direction to go in, looks like it might be multiple deficiencies to me but I'm unsure of how to fix it. Any and all input is appreciated, I'm here to learn!

 

[HandsomeJohnny]

Looks like the phosphorus deficiency I just had. Apparently heat stress can cause it to accelerate. Maybe try lowering temps and giving her a p/k boost?

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[Arthur]

• Looks like Phosphorus temps are fine, rH is OK... A ph/ppm test of the medium is needed. Itll show either a ph slip causing lockout, a salt buildup causing the same, or an underfeeding issue I imagine.

Slurry test. 1 part medium from the pot. 1 part water you use for mixing. Let set for 5 minutes and test ppm and pH.

 

[Moose8810]

• Looks like Phosphorus temps are fine, rH is OK... A ph/ppm test of the medium is needed. Itll show either a ph slip causing lockout, a salt buildup causing the same, or an underfeeding issue I imagine.

Slurry test. 1 part medium from the pot. 1 part water you use for mixing. Let set for 5 minutes and test ppm and pH.

Slurry test is showing 6.5pH and 0.4-0.6EC

 

[Arthur]

Looks like the pH is pretty high. Causing lockout.
Buffer your feeds to the low side and you might give her a flush her till the ppm drop and reset at the correct value.
Why is your water hard? It could be causing the drift over the course of the grow.

 

[Moose8810]

Looks like the pH is pretty high. Causing lockout.
Buffer your feeds to the low side and you might give her a flush her till the ppm drop and reset at the correct value.
Why is your water hard? It could be causing the drift over the course of the grow.

The water I used to make the slurry is my well water. 142ppm 7.1pH, just double checked. I'd read that it wasn't high enough to be overly concerned about, is it enough that an RO setup would be worth it?

Around what pH/EC do you think I should be feeding her at to bring the coco pH into proper range?

 

[Arthur]

That should be fine, I'd run it. Looks like it just drifted over time. I usually check the medium a couple times a run, about flower start, and again about 4 weeks into flower. That way if its moving up or down I get it early before I see it most of the time.

You should be fine once it's set again. And now you know to take a peek occasionally.

 

[Arthur]

If your nutes are recommended from 5.6 to 6.2 I'd run 5.6 for a few days and recheck. You'll want to recheck anyhow, you don't want to over correct. I converted the ec so my old ppm brain would understand the [HASHTAG]#s[/HASHTAG], looks like you were right in the range about 400ppm, just not able to uptake, I'd stick right there. Once the pH comes down and she starts eating, you may need to reevaluate.

 

[St. Tom]

i grow in coco pal in flower on remo newts but it may not be the same as yours but at your girl's age i would be running about a 1.6 to 1.8 also i think it may be a calmag issue but i don't want you going off my advice maybe @Waira could advise you further also @Arthur knows his stuff

 

[Moose8810]

Thanks for the help and the advice! I'd been wondering about increasing the calmag and p/k based on what I was seeing. She's the furthest along of the 6 I've got going, really starting to chunk up so I thought I just wasn't feeding her enough, but wanted to check here first. Going to hit her on the lower end pH wise until it comes back into range then.