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

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
View attachment 3974655
View attachment 3974655View attachment 3974656View attachment 3974655 View attachment 3974656View attachment 3974657View attachment 3974658View attachment 3974660

Those little bottom leaves often do what you describe as the plant doesn't really need them any more but your other problem sounds heat/RH related.

After looking at the pics that leave at the bottom is probably like that from it's close proximity to the soil and I'd just snip it off so it doesn't catch some fungal disease and spread to the rest of the plant. Your humidity is pretty low for the temps and the curling is barely there and is the plants way of increasing heat loss or to help it transpire more water in low RH.

Looking very good actually but be careful with the nutes because with low RH the plant will use more water than it should and pull in too much nutes with it which makes it easier to burn the plants. Tips and margins turning brown is the first sign of nute burn so watch for that. 6-8" from the lights is fine and you may want to get a bit closer as the plants get bigger.

I use a laser thermometer to check leaf temps under my HID light and as long as the leaves closest to the light is 80 or less it's good to go.

Good luck!

Good post above! I would just differ on the first sign of over feeding, it usually begins with downward clawed leaf tips. Unless you drop a pound of guano on her, then you get a complete failure of everything! Lol. Did this once for kicks. Kinda fun.

Put some water down when your leaf edges start going up like that, that's a sign of heat stress and water will correct it. Good luck!