First grow, 1 plant. Very basic , yellow leaves

Hi, I've just put my Auto Northern lights as my first ever grow, extremely basic for now until I get in the swing of things. 1 plant, 1 light, 1 fan.

The past few days I have noticed discolouration in my leaves, what could this be? I'm using 125watt CFL , no nutrients.

My next grow will be slot more organised, trying some easy kush. This is just a little mess about to see what I can do

Thanks for your help

Get a water ph tester, id say your water is your problem

Looks like new growth to me.