What could be causing my Cannabis plants leaves to curl up & turn the tips brown?

[NickPapageorgeyo]

I have two ladies growing indoors under my T5 growing lights, about 6 to 8 inches away from the lights, with a fan blowing on the plants from about 3 feet away. They are currently growing in a homemade mix of soil that includes mainly organic soil, sphagnum peat moss, mineral soil, earthworm castings, along with perlite, vermiculture, and a little Espoma Bio-Tone 3-4-4 for some initial macronutrients in a circle around the water line of the plants. They germinated around June 22nd, 2017, so they're only about 2 weeks old, about to go into their 3rd week of growth. The plants have been growing fairly healthy in my opinion, but this is my first time growing these wonderful ladies. I have kept the temperature between 72-84 degrees Fahrenheit & the humidity between 35-45% under the lights (humidity reads higher when not under lights obviously). My question [after thorough research and reading] for any experienced grower is why my [two] older base leaves have turned brown at their tips & are somewhat 'drooping' down towards the soil? My second question is regarding my 2nd plant, which is growing nice, but has some definite yellow spotting on its' base leaves and its top leaves have been 'curling up' around the serrated edges, making me think it may be a little too close to the [T5] lights (top of the plant is about 5 inches from lights)? If you could let me know your thoughts that would be greatly appreciated!

Also, I have noticed a couple of small bugs on top of the soil & around the plants, which I believe to be fungus gnats. At the moment they don't seem to be too big of an issue, but they bother me & I'd like to prevent any bug from feeding off my soil/plants. Is this normal to deal with and what are the safest ways to stop them from growing besides drying the soil out or putting yellow sticky traps up?

I have uploaded/attached a couple of pictures of both plants (the one with more finger leaves is about 5 days older).

Much thanks & love my friends,
Nick Papageorgeyo

 

[im4satori]

those are some nice looking plants

I don't see anything wrong with them

the leaf margins curling up slightly could be heat, or it could be an extremely mild magnesium def or it could be nothing

the lower growth means nothing really

but im betting its heat or light proximity cuz theres plenty of room to grow and there should be magnesium in that good looking soil you got

theres nothing to lose by spraying them 1 or 2 x with 1/4 tsp Epsom salt .. it wont hurt anything and it might cure your leaf cupping/curl if its not heat related

 

[Borgarden]

Heat/cold/humidity and the grey spot looks like a phosphorous issue which generally comes down to the ph but if you are using organic could come down to the water you are using. Overall the plant looks really good for 2/3 weeks especially considering the size of the pot. The tacoing of the leaves could be heat though, just remember that your temp gauge reads in the safe area but the temps at the top of your plant are different from the temps around the gauge.

 

[cannn]

Heat/cold/humidity and the grey spot looks like a phosphorous issue which generally comes down to the ph but if you are using organic could come down to the water you are using. Overall the plant looks really good for 2/3 weeks especially considering the size of the pot. The tacoing of the leaves could be heat though, just remember that your temp gauge reads in the safe area but the temps at the top of your plant are different from the temps around the gauge.

Phosphorous def always comes with purple leaf stems. Doesnt seem like phosphorous to me. Phosphorous toxicity would cause lockout of multiple other nutes and thats not the case. I agree with satori

 

[Roger A. Shrubber]

i'd try to get the rh up to at least 50% while you're vegging, the lower the rh in your area, the more the plants have to transpire (perspire in people) which is wasted effort they could be putting into growing.
once you start to flower you can drop down to 40% or so to help stop any kind of mold/rot, but in veg they like it a lot higher

 

[im4satori]

anytime I tried to use a humiditfier I ended up with PM

but I don't live in the desert either so just be careful to keep the humidifying device far from the plants