Please diagnose these symptoms

Please help me locate problem... this is the only plant experiencing this in grow tent...

Are you foliar feeding this plant? Looks like it has curled leaves and burned leaves. What is your watering schedule?

Well they are 2 gallon pots I feed them once a week with a mix of 1 liter water/food... and in between I'll spray the grow tent all over with just water. as well as the surface of the pots with same spray maybe once a day..

I would stop spraying the inside of your cage everyday. The extra water/humidity will cause mold and mildew. That size pot would normally be watered three times a week, one of those feedings would be a nutrient solution. Over watering once a week may be causing root rot and other issues.

It's very dry in the tent with lots of air being circulated. don't think there would be an issue of mould.. but u think I should water more in between? I check the pots everyday doesn't seem to be a lack of moisture in them

I live in Colorado where it is super dry and I never mist the inside of my cage. Watering multiple times will encourage better growth than over watering once a week. You don't want your plants to get to dry or too wet. When they suffer from either condition they are susceptible to disease and pests.

For a 2 gallon pots. how much water would you suggest? 1L too much ?

So here is the deal, get to know your soil medium. Water with 1/2-3/4 L and check in two days with your finger or if you can lift the pot slightly and see how heavy it is. This will help you determine your watering amount. Remember this will change as your plants become larger. Find a soil medium that you like and stick with it for consistent results. I use FF Ocean forest, which does not require any fertilizer be added to your water for the first 4 weeks.

Do you check the PH? for the foliar feeding too.
Its hard to tell what it is for sure, but I would suggest that you stop spraying water, see what happens. Every plants is different in a way so maybe this one is the only one showing the signs.
Also, check these links maybe they will point you in the right direction:
http://www.growweedeasy.com/ph-fluctuations-cannabis

ps. Ph fluctuations look a lot of root problems!
I hope this helps! Keep growing!