Seedlings stage yellowish leaf color!

[Erni2019]

Hi,

I am new here and looking for help with my first garden. I noticed a change in color with the leafs in my seedling stage, where i am now. I am watering them once every 3 days , 150 ML a day with pH between 6 and 6.5. The lights on top of them is 18 inch height. I am keeping a 72 F average temperature and 65 Humidity. I attached some pictures, this started with one and now it spread to 3

 

[Chris Scorpio]

Why every 3 days??

Arbitrary number, dart bds??

Water when they need it, I'd say more often than 3 days

I'd say you have stressed them a bit

What's the soil? Any nutes yer adding

Also led usually are at 24" or more for seedlings

 

[Erni2019]

3 days because I read online about watering every 2-3 days and I wasn’t seeing signs of underwater. However, the soil(Attached a pic of the soil below) would be very dry when I water. I can reduce that to every 2 days if you recommend. To be honest, I thought I was over watering and this is caused by root issues. (Sorry but not sure what dart bds means)

I started the seeding process in a seeding tray (see attached) and then moved them to a X by X inch after 4 days.

I have the led at 18” because that’s what I read. Should I move it to 24”?
The current size of the pot is 3.5 in *3.5 in

When we first started we used the following:

And this is the current soil: