Brown discoloration on leaves

[Fortuno]

This is Sweet Zkittles from RQS, week 9 of veg. She's under LED QB light in 15 litres fabric pot. I'm using BioTabs nutrients which consist of tabs that you put into the medium at the beginning, organic fertilizer and some fungi/bacteria to improve the soil. I'm using manifolding and some light defoliation to uncover fresh growth tips.

I noticed some discoloration on leaves. Also, new growth seems bright green.

I'm watering with tap water every 4-5 days when top 1 inch is dry. It says in the instruction that with those nutrients there's no need to regulate ph and ec.

Any insights on what could be wrong? Is it some kind of deficiency?

Pics:

https://imgur.com/a/0luF2Cr

[Rwise]

I see some crooked leaves which suggests bugs, look at the underside with a 30X lens.

[Korn]

I agree with Rwise. Bugs or no bugs I would do at least a 20-30% defoliation of the big shade leaves to open the plant up. If you do find bugs, spray them down with some half strength neem oil. Check a few days later and repeat if needed. Plant appears to be young enough that neem won’t be affecting much bud material.