Concerned about two plants.

Hey what's up guys? Let me first explain what is going on here. I'm a first time grower, running into a few problems. The first mistake out of many I made was listening to advice from a fellow friend who happened to be a grower. In the beginning I listened to everything he said and bought what he recommended, etc. However, after some things started going wrong, which you'll see, I decided I would come do a little research myself. The problems have been going on for a few weeks as the plants are about 3 weeks old and the "burn" or w/e it is started about 1 1/2 weeks in. Bottom line is I'm here now doing research and trying to get some help from you, so anything you have to say will be greatly appreciated.

The first plant you see, and you have to excuse the bad picture, i'm super high right now, but that first blurry one is one of the leaves, it has the same coloring as picture #2, but it is curling up, my camera had a hard time focusing . In this plant I'm using some off brand P.O.S. soil that's just soil from a Big-Lots in the area. There are no nutrients in this soil so I'm wanting to think this is a Potassium deficiency which would be remedied by putting some Banana in the soil? Or is there a better low-cost way I don't know about to deliver the K needed? What is the deficiency there do you think?

The next plant, the first picture is of it's bottom leaf set (1 leaf) and the next picture is the 2nd node. Any ideas whats going wrong here? I'm fairly certain this is Nutrient burn because as I stated earlier I listened to a friend of mine who I thought was knowledgeable and we bought MG soil and MG nutrients that weren't water soluble and mixed it in with the soil....I don't really have anything else to say on the matter because I realize how stupid it was, I'm just looking to remedy it. I've flushed the soil one time already, should I do it again do you think? As you can see in the pictures the next set of leaves aren't that bad, but I feel like they are getting there, I could just be paranoid.... Any help would be very very appreciated.

Sorry for the length, I'm high and I want a legit answer because I'm skerd haha.

TLDR: I'm stupid and listened to a friend who didn't know shit. Now I have two plants with BS deficiencies and I can't identify them because I'm a noob. What are they and how can I fix them <3?

Hmm, not really sure what's going on there, but i'll give ya a free bump.

Definitely nute burn. I have a pic here of pretty badly burned plants and they look very similar, rusty brown spots and curling. I don't use MG soil but have heard if it's the time released fertilizer kind it's not going to work well. If that's the case, you wanna stick with just plain water until the plant turns light yellowish. That's how you know it's hungry for nutes. I have a pic of hungry plants too. Hope it helps.

Alright, thanks a lot man, gonna just give them just water for the next few days and see how things pan out.

Potassium.Please stay out of Big Lots for your gardening supplies,go to Wal-mart.

Your leafs are curling under a little,potash deficient.KEEP SMOKE ALIVE!!

I appreciate the help, like I said, I didn't purchase the soil on my own accord, I listened to a friend who I thought was "wise", I was incorrect. I appreciate your advice though, I'm looking to head to the hydro store today to go buy some nutrients.