Help - sick plant yellowing

Hi Chaps, having some trouble with my grow. The tips of the larger fan leaves have started to turn a paler color (green/yellow) towards the edges of the leaf blades (away from the veins). The plant has just been put into bloom for about 8 days and appears on the more recent growth but is only really noticeable on the larger leaves. I'm thinking a deficiency of sorts. Any input welcomed.

Plant details
Strain: Chrystal Nirvana
Height: 70cm
Grow conditions: 400w HPS Son T Agro (appox. 30cm above top), Temps: 18 - 28 c, Humidity 55 - 70 %
Medium: Coco 90 %, Perlite 10 %
Nutrients: Growth Technology (GT) Coco Parts A & B - approx. 62.5% of full strength
pH: untested
Age: 11-12 wks overall, approx 8days into flower
Grow room:1.0mx1.0mx1.8m

Sorry about the poor pics - VGA lens

Hey man, have you ever had that problem before? Your ph is untested, probably a good idea to start there maybe. Not sure if I have any more useful info that that lol. I know it's not much man, sorry. I don't grow coco though and haven't done any research on it so I don't wanna tell you something fucked up. But maybe it could be possible that accumulated high or low ph stays in the medium? I would have also suggested that maybe back off the nutes just slightly, but you've already been growing it for a couple months so I'm thinking you have that beat. Is it possible to over water with coco? Sorry if I'm just spilling things, but that's how I get through problems like that, think of everything and troubleshoot. Air, water, light; right? Also considering your plant seems to have the same coloring from top to bottom in places it's safe to say it's not heat I think. Are you spraying foliar in the light?
I'll stop there man!!! Hope anything might get the old gears crankin' anyways!! Good luck!

Thanks 4 the reply. No I haven't ever had this problem before or any other problems apart from pests that's why I never bothered to test for pH. I'm a bit of a habitual over-water-er though so maybe that's part of the cause. No foliar sprays are used. Last day was given a mild nutrient solution but now I'm thinking more that it's a nute deficiency than a possible toxicity. Maybe someone with a keen eye for these thing can shed some light.

Decided I'm gonna try half strength nutrient solution for next few days. Come on guys any ideas what the problem is ? Any input would be greatly appreciated !!!

crappy pics. forget going half nutes at moment, get a good ph meter, get it to 6 ,wait a week and they should be ok.

Did some pH testing seems OK around 6.5. Now noticing some purplish coloring on some of the leaf stems. Also there are some blotches of moisture that appear on leaves even though i don't water from above. Starting to think I have some sort of fungus like Gray Mold (Botrytis) . Any one have any further opinions on what this may be before I take drastic measures

trontreez said:

Did some pH testing seems OK around 6.5. Now noticing some purplish coloring on some of the leaf stems. Also there are some blotches of moisture that appear on leaves even though i don't water from above. Starting to think I have some sort of fungus like Gray Mold (Botrytis) . Any one have any further opinions on what this may be before I take drastic measures

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Purpling can be 2 things, genetics, or phosphorus deficiency. It often gets mistaken as a (P) problem, when it indeed is genetics. If ph is fine, and you have been feeding it (p), than look at other plants, if they don't show the same look and are fed the same, it might not be a problem. As far as the 2nd problem. Whats your humidity like? Is the plant in question growing real large leaves, compared to others in the same setup? It don't really sound like a problem, plants do perspire, but if humidity is too high, they may perspire too much.

Unfortunately I have only one plant in the set-up so I can't really compare it to any others. The plant was vegged outdoors and the leaves only started to get a lot larger when it was put indoors to flower (not sure what this means). As for humidity it gets as high as 70% sometimes and as low as 40% but most often around 60%. In any case I got paranoid and put it back outdoors and crossing my fingers that it doesn't re-veg or go hermie. Starting to doubt that it was bud mold as well. Thinking it was just a Phosphorus deficiency all along. Man do I feel stupid.

Thanks for all replies. Keep ya posted if all goes well.