I had something that looked exactly like that. My son said it was powdery mildew, but Google Lens said it was this type of lichen that grows on trees.
I source some soil and mulch from the forest I live in and am thinking that cannabis is somewhat resistant.
Hi wotcha, im no expert at this kind of thing, but would have thought possibly phosphorus deficiency. I used to use citric acid as pH up when i used my tapwater… but these days i use rainwater and that seems to be better overall if you can get it. If the soil is a bit cold that woudn’t help either.
VG
Throwing up a couple of pics at day 25 of flower. All plants stacking nicely.
Full tent
C4DD4
Contra D
I gave them a dose of Plagron Green Sensation (0:9:10) which seems to have stopped the issue with the leaves.
Watering once every three days now, with 5ml/l Plagron Alga Grow and 15ml/l Plagron Alga Bloom
Looking great ! - interesting to see them side by side… are there any big differences atm? the buds on the Contra D perhaps look a little taller from the pics?
VG
Calcium def maybe , I know you hard tap but maybe
I have hard water too but will still supplement with cal mag at 5ml / gallon. I find if I don’t, they get deficient in week 2
Cuz calcium in tap but it’s not good / avail to plant
It looks like a bit of nitrogen deficiency.
Thanks for all the suggestions everybody. I think it must have been a phosphorus or potassium deficiency as a couple of doses of Plagron Green Sensation put a stop to it.
It’s hard to tell much difference at the moment as they’re all so packed in, visibility below the canopy is limited.
Height wise the Contra D’s are all very similar. The C4DD4’s are all a little taller, I’d guess between 4" and 8". I think bud development on the Contras is slightly better at the moment, but some of the C4DD4s look very promising.
Lots of crystals covering the sugar leaves, which give a nice variation of smells when squished. My favourite smell so far is sort of sulphury and bitter, just like brussels sprouts. Is this the tell tale chem smell?
I’ll try and make time this weekend to take some pictures of the individual plants.
Couple of bud pics in the mean time, interesting double top on one of the Contras. The yellow tint on the leaves is just the camera.
looks to be coming on really well! - the Contra D has long pistils…
brussels sprout is bang on one of the classic chem smells! - i grow them in my garden too lol.
along with a sweaty gym socks smell, onions, garlic. Sometimes the D smells pretty much like sh1t … in a good way. D also has a pine background note that can get amplified in the odd pheno and i think has come to the front in some Contra D phenos.
The 4 i don’t know so well, but has more kushy notes , still the pine and some say lemon IIRC.
VG
Thanks @VerdantGreen I’ll have a good sniff this weekend now I know what to look out for. Unfortunately “kushy notes” means nothing to me - can it be described using smells of non cannabis things?
Also unfortunately, I do know what sweaty gym socks smell like 
Woot, I missed your thread but now I’m hooked. Have some contra D to test too, so that’s cool to see another grow. They’re looking really nice, hope you find some keepers.
for Chem 4 it is kind of peppery and a bit more earthy… but still a very recognisable Chem funk.
Any updates @Wotcha ?
Strapping in to follow this / see how this ended as I have just ordered up some C4DD, C4DD4 and Contra-D to run at some point in the future.
I am thinking a cross to Twin Peaks (chem91 x chemsis) will throw out some gems maybe! 
I also bought the breeder pack and I’m very happy with the outcome of both Contra D and C4DD4. The Contra D is a very good breeding tool. Especially the “large” phenos of it.
The C4DD4 wasn’t really chemmy but a very nice plant indeed.
I have photos scattered around the site and can be found with the search function. Hope you’ll enjoy them as much as I have.
Pz 
I will hunt them down after I grab a cup of tea OC, Thanks for letting me know. 
Ofc! Happy to help out, I’m still waiting for more people to discover @VerdantGreen s amazing Chem work!
Pz
I have his Ahmar as well He’s a good lad and I am not scared to say that alongside Verge from UGORG he is one of the UKs best breeders 
Zero BS with @VerdantGreen his Herijuana repo years and years ago provided a cutting that helped me manage chronic pain for over a decade.
I couldn’t agree more, I would say that he’s probably one of the top boutique breeders in whole of Europe!
Pz
