Leaf Problems

Ok.. so, i have 3 white widow plants that are exactly 13 days old as of today, up untill now they were doing fine, but now the leaves are turning yellow/brown and even WHITE (ish), it can't be nute burn as i haven't given them any nutes as the medium im using has all the nutes the plants will need, im using ''biobizz all mix'' a little info on the medium:Organic Soil
All-Mix was developed especially to be the best potting soil for organic cultivation. It consists of 20% sphagnum peat moss, 35% garden peat, 10% high quality organic Worm-Humus , 30% perlite and 5% Pre-Mix.


I'll upload a pic (this isn't of my plant) its simply just to show how it starts off (tips and edges turn yellow/brown then spreads throughout the whole leaf turning yellow/brown/pale white-ish) i planned on using a sylvania growlux flourescent tube for the 1st 2 weeks, and this is the light i have been using, then i planned on upgrading to cfl's for the rest of veg and for flower hps or mh or HID (haven't got that far ahead as of yet) anybody any ideas? I have a few ideas what could be causing it but i can't seem to find the specific reason, things that automatically came to mind where: heat stress (been in the 80's past few days), not enough air circulation (but through the day they are outside and when brought inside to my grow area they have 2 desktop fans on them constantly) nutrient deficiency (surely at 13 days this can't be a problem?) the list goes on, i have a lot of knowledge on cannabis cultivation, allthough i've not grown many times, (currently only my third grow) but obviously there are people out there that know a hell of a lot more than me, so if your one of them people, PLEASE spare a few minutes to take out of your schedual and say a few words, thanks in advance for any help/suggestions.

the browning of the edges on the leaves of your plant is a good indication of heat stress.

I know that allready if it was just the browning of the edges i would have this done and dusted, its the 2 together thats got me thinking, as the leaves are yellow AND brown, they are showing multiple problems but cant be that bad as they are only 13 days old and the problem only started a few days ago, n, p, k, mg, zn, mn, it could be any of these or heat stress or basically anything i need someone with a lot of experiance

https://www.rollitup.org/general-marijuana-growing/1469-marijuana-plant-problems-cures.html


there is the same picture originally attached under figure 2 of nutrient solution burn.

It can't be nutrient burn as i haven't given them ANYTHING, just germinated them and potted them and give them water, i have been spraying the leaves with a mist though i think it might be that because its been real hot i didnt want the leaves to burn, tryed cooling them down with a mist forgetting its like humans putting baby oil on then sitting out in the heat, burning is going to be a problem i think this might be what it is but its spread through more leaves now (that i haven't sprayed) haven't sprayed for a day or so now and it's still happening, also im going to try 2 tablespoons of epsom salts with a gallon of water see if it helps any