hi all over the past few days i have noticed my leaves are going down hill, i noticed it on 1 or 2 plants and it is starting to spread to all of em :-( i am ready to flower in 1-2 weeks and would like to get this problem sorted out, but i have not a clue what the problem is, does any one have any ideas of what is going?

right this 1st pic is the worse of the nice leaves it has affected

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this pic is of the worse of the smaller leaves

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and this last pic is of one of the lowest leaves, i dont think there is much problem with this one as it is not getting much light so i think thats why its gone yellow due to lack of light, the main problem is leaves 1 and 2 which seems to be spreading to other plants and leaves :-(

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Please if any one knows what is going on here and how to sort it out you would be a life saver, thanks

EDIT:
Some extra info to help decide on a solution:-
I have not started to use any nutes, as i will start to use nutes when i switch to flower, just been using plain water settled for a few days.
lights on temps are between 26oc - 28oc RH between 30-55
lights off temps are between 230c - 24oc RH between 45-60
Using 600w sodium about 15 inches away from canopy, i could get a lot closer due to my air cooled light but do no want to lose light spread

also here is the back of the leaves of 1 and 2 sorry only leave 1 i can do the other pic is too big

back 1
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cut all the affected areas out
take all yellowing leaves off , quickly before it reaches the main stem .

Thats exactly what i've been doing this morning to my little devil
Just remember to try and keep everything as clean and sterile as poss. I wipe scissors with alcohol wipe first.

so u think its a disease then? dam man :-( wonder how it started grhhh

I've got similar to that (not as bad as that tho') and cut the affected leaves off, I've also used Epsom Salts which seemed to help and Ganjacat thought it might be a nute prob.

thanks bhang, so when u cut the leaves off shall i just cut the tips off which are affected or shall i cut the stem off? also with the epsoms did u spray or feed with epsoms? oh im not using nutes yet so cant be that

found out the problem from a very very long time grower friend of mine, and it is burn from when i water and get water on the leaves sometimes, also i have got a dehumidifier in there which is gettting quite a bit of condensation on the plants closest to it thus causing the burn effect, glad i have not got a disease tho and no chopping is nessessary i am thinking about raising my humidifier above the canopy so the surrounding plants do not get affected by it

the plant looks hungry?
how long has it been in the pot, how fast is it spreading, from bottom up

settling water raises the ph and ec? that i am admitidely unsure of myself

just some ideas, could be wrong but im feeling chatty today

hey dam, thanks for the info, they are not hungry they were only potted up in new soil a week and a bit ago, them leaves were just a few off the bottom ones that got wet from watering and the humdifier which caused them to burn under the light. yeah mate my water comes out of the tap at like 7ish pH and after its settled for a few days the pH rises to 8-9ish but you dont need to worrry about pH in soil as the soil buffers it down any way and also i dont worry about the ec where im in soil, i just follow ot's bb guide for nutes and its working a treat