White Moscow- Sudden leaf wilt

[Loam Haystack]

Problem: All of a sudden, my Auto White Moscow (day 40'ish) has had a few leaves go partially brown and wilt. I am micro-managing this plant and didn't see this coming until yesterday I was out for the day and came back and it was like this (pictured).
Medium: Coco with 15% perlite and 15% vermiculite (some of my other strains from this grow have suffered mild CaMag deficiency which I think is from acidity of coco. I have been correcting this manually with Calmag in every feeding and slightly upping the pH for every feeding for the past ~20 days (perhaps this is the mistake?)
Feed: Pictured. Still using veg nutes @ pH 6.8-7.1 (runoff 6.1 to 6.3).
Strain: White Moscow, day 40 from popping through soil.
Climate: Dry warm climate, outdoor grow - max temps daily 25-27C lately. Sunlight 8am - 5pm, then taken indoors to rest at night rather than face the cold night air.
Additional info: I have been feeding with every watering, every 3-4 days before the coco gets dry. Could this be nute burn? Other leaves seem unaffected. It's limited to just 2 fan leaves and the very top of the main cola.
Pics show the entire plant looking droopy - that seems to be normal for this plant at night (which is when pics were taken). It wakes up every morning.
Pests are not a problem.

Pics should be self explanatory.

Hope you guys can help tell me what I'm doing wrong!!!
thanks so much,
Loam
/edit forgot to add pics of nutes.

 

[Waira]

Have you grown in coco before, and are you savvy with it's unusual CEC characteristics? It's a great media, but it's sooo not soil! treat it as such, and problems are guaranteed,.. One of those is it's huge binding capacity for Ca, which until sated, will keep it from the plant (good thing you've started adding Ca-Mg in); pH is wrong for coco, which should be upper 5's to low 6's- in-pot; testing the straight run-off won't give accurate pH, but will indicate if it's badly off, which I think it is; off pH will screw nute availability up! ... Do you check the ppm's (EC/TDS) of run-off? To see what nute load is building up in there? Huge impact on pH there,... Anyway, the symptoms look like nute burn, including the somewhat crinkled newest growth, but the whole plant looks pale, and lanky...long term issues there,.. So, an accurate in-pot pH is needed, and ditto for run-off ppm's... if a flush is needed, it has to be a specialized one for coco, to try and reset that CEC balance and purge the excess at the same time,... here's a link for an "improved" run-off pH test and calculation.. this method in general is iffy, but this one at least addresses some of the error sources: https://www.autoflower.org/threads/...-for-run-off-testing-and-ph-estimation.41733/
... try it out, unless you have a good quality pH probe (Accurate 8 is a good one)

 

[Loam Haystack]

Have you grown in coco before, and are you savvy with it's unusual CEC characteristics? It's a great media, but it's sooo not soil! treat it as such, and problems are guaranteed,.. One of those is it's huge binding capacity for Ca, which until sated, will keep it from the plant (good thing you've started adding Ca-Mg in); pH is wrong for coco, which should be upper 5's to low 6's- in-pot; testing the straight run-off won't give accurate pH, but will indicate if it's badly off, which I think it is; off pH will screw nute availability up! ... Do you check the ppm's (EC/TDS) of run-off? To see what nute load is building up in there? Huge impact on pH there,... Anyway, the symptoms look like nute burn, including the somewhat crinkled newest growth, but the whole plant looks pale, and lanky...long term issues there,.. So, an accurate in-pot pH is needed, and ditto for run-off ppm's... if a flush is needed, it has to be a specialized one for coco, to try and reset that CEC balance and purge the excess at the same time,... here's a link for an "improved" run-off pH test and calculation.. this method in general is iffy, but this one at least addresses some of the error sources: https://www.autoflower.org/threads/...-for-run-off-testing-and-ph-estimation.41733/
... try it out, unless you have a good quality pH probe (Accurate 8 is a good one)

Thanks so much for your detailed response, Waira!!!
No, i'm not terribly savvy with coco.. I did a grow last year with it and all went 100% fine (except for a hail storm..but hey). This year I thought things would be equally easy but I can see now that different plants require different things.
I can't believe I haven't read your pinned post you quote above. Will try out the "improved" method ASAP. I can grab an EC meter tomorrow as well. Hydro store not too far away (although the guy there told me "you shouldn't need one when growing in coco").

I'm really concerned about my plants being "pale and lanky" as you mention. Any ideas what I'm doing wrong there? seems to be a common theme among all my plants, both this grow and last year's (see my signature) even though last year the bud quality turned out perfectly acceptable for me. I'm posting a new pic here - this is the same White Moscow from my post yesterday, but a couple leaves today look like this...not good I'm assuming....eish!

Again, thanks so much for helping me out!

 

[Waira]

Hey, I'm not a coco grower either, but several good mates are, and I've had a crash course at least here on dealing with it's common problems folks run into,... Read up here, and Canna Coco has a great website with lots of articles on it... I gotta disagree with your store guy on the TDS or EC meter,.. they are valuable tools for testing and managing your nutrient strength, testing your water, run-off if needed, etc.,... this is critical in coco, as it is in hydro! I'm not sure coco is the best choice for outdoors,...
... the plant looks long term underfed, or pH problems making nutes partly unavailable,... Si supplement is also a very good thing to have, since you're not in a soil... Si has many benefits, including making the plant tissues tougher, stronger and more resistant to microbial attack and heat tolerant,.... if you stay coco, get coco dedicated nute's which are made to deal with coco's CEC properties... that leaf looks N defc., possibly S defc.,... after a point, symptoms kinda become muddied together....

 

[Loam Haystack]

So popped in to the shop, got myself an EC meter. Turns out what I was most likely doing wrong was not pH'ing my water down. Nute/feed going in was usually between 6.8-7.3 pH @ EC 1.8-1.9. I was keeping pH high because I thought the calcium was being locked out from the acidity of the coco (I wasn't fully understanding how pH requirements of coco are different...and would I be correct in saying that it's not necessarily the acidity of the coco that causes a problem with Ca? The correct way to combat Ca deficiency in coco would be to keep pH sub-6.0 but introduce supplement?)

Anyway, I did your run-off method with RO water and turned out that I had some pretty gnarly runoff EC so I flushed, and began feeding @ sub-6.0 pH and I'm also including some MgS04.
Already I could swear my plants have all gone a few shades greener and are starting to bulk up considerably, and the yellowing from the previous picture seems to have abated (but not disappeared...I'm assuming the damage is done and will not go away).

I'll get some pictures up in my grow thread, but looks like you really helped me get back on track, @Waira!

 

[Waira]

:smoking: indeed, coco's odd Cation Exchange capacity involves powerful preferential binding of Ca to it's particles, so that must be sated first, or it'll hog the Ca from the plant! pH affects availability as well, and should be upper 5's - low 6's,... Always water with at least Ca-Mg, mild doses to help maintain this Ca baling act... go easy on the epsoms, maybe a couple rounds and that's it, 1tsp/qt usually, but with Ca-Mg going in as well so cut that in half... Well done on the correction mate, it sounds like you had salt build-up which can be insidious until it all crashes at once! For coco, I read that a flush solution is best made with RO, plus 150ppm Ca-Mg, and another 150ppm of nutes, pH 6.0... pour through until the run-off is close to input ppm's,... this "resets" the CEC and purges the excess,...

 

[jingo]

Glad you figured that out I was reading from the start hoping you got the pH thing down. Do you use R/O water for all your mixes or just your flush?

Reason I ask is I do coco with R/O and I'm considering chloride suplimentation since it's not present in R/O water. I haven't found established levels for cannabis yet and id have to contact GH about they're coco and see if they'd provide the chloride content. I know Cana Pro tested about 50 ppm chloride in the US, which is probably about half what i want in flower.

Hydro growers and rockwool growers would have zero chloride if using R/O water. Some municipalities have very low chloride also.

Anyway, food for thought

 

[Loam Haystack]

Glad you figured that out I was reading from the start hoping you got the pH thing down. Do you use R/O water for all your mixes or just your flush?

Reason I ask is I do coco with R/O and I'm considering chloride suplimentation since it's not present in R/O water. I haven't found established levels for cannabis yet and id have to contact GH about they're coco and see if they'd provide the chloride content. I know Cana Pro tested about 50 ppm chloride in the US, which is probably about half what i want in flower.

Hydro growers and rockwool growers would have zero chloride if using R/O water. Some municipalities have very low chloride also.

Anyway, food for thought

Hi Jingo!
No, only used to flush - no R/O water @ my place and so I just ended up buying about 40L as a once-off. Tap in the area typically contains chloride ~10-12mg/L according to what I can find (if you even wanted to know?!)
Cheers

 

[jingo]

You would probably benefit from calcium chloride in flower to get the most, although like I say I'm just starting research. I'm thinking 50 ppm for veg and 100 ppm for flower. Would be a good target for chloride levels in cannabis.