Leaves edges turning pink?

[KillerShroom]

4x4 tent----1200w KINGLED--- VEG week 6---5 gal. fabric

I just noticed this today.. You see the pic. Edges of a leaf are starting to turn pink. one other leaf is JUST starting to do the same thing. I'm sure one of you knows right away what the issue is.....upon my research i can't tell if the deficiency is zinc, potassium, or sulfur. Maybe it's nutrient burn ??

Also, as you can see i am getting over a minor fungus gnat infestation.

My concern is, because i'm using 'KIND' (brand) soil ( compost ) with Fox Farm on top as a buffer, I'm not supposed to add any nutrients, ever, as per the manufacturer, so if this is a nutrient issue I could mess up the soil composition if I add anything.

I have been accidentally using phosphoric acid to balance my water PH which I just learned I should not be using. My tap water is really good; only around 7.5 PH ( and 22 PPM ) so i don't have to change it too much. I just went and got some citric acid to use from now on.

If you notice the plants look a little droopy is because it's almost lights out AND tomorrows watering day so they're a little dry.

Any help on why my leaves on one plant is starting to turn pink would be awesome !!

I'm also open for any other tips you guys have because I am a first time grower.

 

[FelipeBlu]

Welcome to

Lower leaves showing edge damage - likely K def, but still relatively minor. You could try a kelp product with a nice amount of K. Foliar would help address it immediately.

 

[KillerShroom]

Awesome. Thanks! I’ll grab some kelp meal and add it to my soil before watering today. I’ll foliar feed later if need be.

 

[Bush Doctor 77]

Awesome. Thanks! I’ll grab some kelp meal and add it to my soil before watering today. I’ll foliar feed later if need be.

Welcome. Lose those yellow gnat traps, and get some BT to control them. I use crushed mosquito cakes mixed in the top 3 inches of soil when I put them in pots.

 

[Bush Doctor 77]

Welcome. Lose those yellow gnat traps, and get some BT to control them. I use crushed mosquito cakes mixed in the top 3 inches of soil when I put them in pots.

...and BTW, overall, nice looking plants.