The first set of leaves (water leaves) will go yellow an drop off naturally. The second and third leaves look fine though. Are you using a seed and clone nute mix?
I have Iguana Juice I added 1.33 OZ for 10 Gallons according to Advanced Nutrients Calculator for a total of 497 PPM, my PH is 5.0-6.0 it fluctuates do to my larger air pump than required... im thinking about disconnecting one of the air feeds to slow the PH rising. This is my 4th hydroponic grow, took a 2 year break and i'm trying to get my high time quality 100% organic buds back