Slight pale patches on first set of 7

One of my babies has just the slightest little pale patch on its first set of 7 leaves. I looked up all of the nute deficiencies and didn't find anything that matched so I am afraid it might be ph related, but I still havent gotten a meter yet. She's just about 3 weeks old. Does anyone have any ideas? I'm about to go take a picture

what is your medium? ph is def a must, get a meter asap.

Potting mix.I have npk and most trace elements covered but I can't get my phone to send the picture I will have to wait till I get to my computer. Where is a common store I can go grab a meter from?

Her leaves arent drooping at all she looks strong and healthy but those little imperfections are bothering me