First ever Grow, a few questions on fungus gnats, powder mildew (treatment), and leaf discoloration

So backstory, i recently started developing a powdery mildew problem, so yesterday i wiped every leaf clean and sprayed them down with a water/dishsoap/veg oil/baking soda mixture. Every since being transplanted a week or so ago, I've worried about fungus gnats, as i read a bunch of scary stuff about Fox farm Ocean forest AFTER i had transplanted them and had seem weird white clumps in the soil. sure enough, a few days later i saw an adult, so i ordered nematodes off the internet to kill them and those just arrived yesterday, so they went in with the watering.

So a few things happened over night, hoping i can get some input on things.

1. Though the powdery mildew does seem to be gone, knock on wood, it looks like the treatment may have slightly damaged my plants? If so im not too concerned because it's nothing they can't bounce back from (hopefully) but i want to make sure that that is infact the problem. The thing is, It looks suspiciously like nute burn, though i cant think of how that would be possible. Any other ideas?
   
   
2. I see a few more adult fungus gnats than yesterday, 3-5 in one plants crawling around on the surface. I'm going to get a bunch of perlite today because i need it anyways, and cover the top 1/2 of soil with it. I heard that you can use perlite OR sand and since i need perlite i was gonna kill 2 birds with one stone, but does sand not have an added benefit of cutting them up? Or is that one diatomaceous earth? I have yellow sticky traps out and literally just have my fingers crossed that the nematodes i fed them the other day were actually alive, otherwise, i've essentially done nothing about my gnat problem yet... any suggestions? How long till i can tell if the nematodes worked?
   
   
3. This one plant, a different strain than the others, looks like it may have a mag deficiency? That's just what i arrived at from a quick "diagnose your sick plant" online thing. Could that one maybe have a gnat problem bad enough it's unable to get nutes? wouldn't my other, larger plants be showing it fi the medium was mag deficient?

Thanks for any help ladies and gents

every plant is different in its own right even if you have the same strain for all your seeds they will still be unique in their own way. that being said one could of been slightly better where the other one was a little more prone to mag deficiency but the treatment could have caused the yellowing and or the nut burn but nut burn isnt too big of an issue as long as you flush good. for the gnats i had a few in one of my pots early on so i was luckily able to just dump the soil and replace it without having to worry about snapping any roots and that solved my issue at least.
http://www.growweedeasy.com/magnesium-deficiency-cannabis

Hey guys! So the powder mildew is gone! yay! There are a few fingus gnats but they are mainly under control and once we transplant we will use gnatrol and gnatnix.
So no im wondering if people could give me feedback in general? See if i have any deficiencies etc
I THINK the edge burning is from my powder mildew treatment and not nute burn, but what do i know.

http://imgur.com/a/y20Z2 https://streamable.com/rsj9i

any tips would be appreciated! These photos are a few days old and the plants have since been switched to a 1000w hps bulb and spread apart from each other a bit.