Dinafem Cheese XXL Auto - New Growth Yellow (and burnt tips)

[Life_On_Mars]

Just took this to try and really show the lightness of these leaves - once I took the pic I noticed the browning on the leaf edges, and also noticed the the very top sugar leaves are not actually super pale, it's the buds newer supporting fan leaves that are really yellowing.

The burning along the leaf edges is making me think it's actually EXCESS calcium, causing the nute burn look, but also locking out stuff like magnesium or potassium?

My tap water is very hard, and I've been adding calmag (I did this after hearing that all LED grows will need supplementing with calmag, especially with long light periods like you have with autos, now I'm not so sure...). Maybe they're hungry for other nutes, but overdosed on calcium?

Here is a top down pic of a different plant from this grow (same strain but different pheno I think) that is NOT showing yellowing, for comparison -

 

[Life_On_Mars]

Gave them some epsom for a mag/sulfur boost a couple of days ago, as well as a feed, she's still growing but also still fading. If the epsom salts are the answer, then how long could I expect it to take for them to 'kick in'?

This is all one plant, and it's the main one showing issues. I know it's not like it's doing terribly, but I can see it lightening up day by day, and it's the frostiest of the five packed into my 4x4 tent, so it'd be a shame for it not to reach it's potential!

Lower leaf - Mag def right? And possibly a bit of cal def too? Bear in mind this definitely started at the top, at the new growth. The tops just started really lightening up, looking more like a sulfur def than a mag def.

Checked the soil PH when I first saw the issue - it was just under 7, which I know is technically OK but also a bit high (and could be potentially be locking out magnesium if I understand correctly) so I lowered my water PH from 6.5 to just over 6 and filled the water tray with that. The soil is now sitting at just over 6, so I slightly overcorrected I guess! I'm assuming now that I give I'm giving it straight forward 6.5 water again it should even it back out.

Since I did the second orgatrex/bactrex feed (as per the biotabs instructions) I've been feeding with Bio PK5 5-8 and a splash of orgatrex, once a week. However, I think it's important to note that I've whilst I've been mixing them as recommended, I haven't been giving a full water feed, I've just been giving the plants a litre of the ferts each (slightly distributing extra to the ones that looked hungrier). However, they're probably drinking about 3-4 litres of clean/calmag'd water a day, so the feed I'm giving them is a good 2/3 times less than recommended. I've always heard 'half strength for autos' and I already had the burnt tips, so I didn't want to overfeed them. Plus the plants are sat in the water trays and bottom feeding, so I can't add the gloopy organic liquid nutes to the tray as it will just gunk up.

Is it possible that this could be -

a) They just need a proper feed? The lime/yellow colour did come through towards the end of the stretch, when the plant was growing extraordinarily fast.

b) It's actually just fading out and heading towards the home stretch? It seems unlikely at day 53, but this one plant did seem ahead of the others, it sprouted faster, hit flowering faster, and frosted up before the others...

According to most other grow diaries I've got about 3 weeks left on these ladies, as it even worth faffing around with flushing etc trying to fix things now? Or just up the feed a bit and hope for the best?

Thanks!

 

[Life_On_Mars]

So... I noticed that the yellowing was all in the spots where the light was strongest, the colas round the edge are less affected (even tall ones with plenty of new growth), so I downloaded a LUX meter to my phone and had a scan around - the areas with the most yellowing were getting a around 110K lux, which I understand can be more than enough to cause light stress on some strains. My 480w LED was at around a 12-14 inches. I've raised it to 18 inches, so they're getting about 70-80K now, which is in the safe range as I understand it.


I've been looking up light damage, these are not pics of my plants, just examples of similar light damage -

The fading on that last one looks very similar to mine in the way it progresses downwards and is concentrated in certain spots (minus the droopiness, thank goodness).

I know this doesn't explain the damage on that lower leaf, but I did have to hunt around to find that - most of the lower leaves are green and healthy except some of the ones that are fully hidden by overcrowded canopy above, and those just seem to be slowly yellowing out naturally. It would make sense that it happened just after the stretch too, as I had the light at around 24", and let the plants 'grow into' the light.

The only thing that doesn't make sense is that there are three other plants (same strain) that are much taller, and aren't showing signs of damage (although they are 'praying' pretty hard, which I can be symptom of too much light) - however those three are clearly a completely different pheno than the two that are showing symptoms, so I'm assuming there's a chance they could just be less light sensitive?

Could it be that this has all just been light stress?!

 

[Life_On_Mars]

In case anyone comes across this thread with similar issues looking for help - Update to this here -

https://www.autoflower.org/threads/dinafem-cheese-auto-xxl-day-43-frosty.78865/page-2#post-2310886

TLDR - my soil probe PH tester is utterly inaccurate. I will be sticking with a soil slurry test with distilled water and a calibrated PH pen from now on. When I did this it showed me that my PH was far too low - around 5. I've flushed them. My soil probe PH tester was telling me my soil was too alkaline.