Brown spots on Young plants help please.

I am growing Hydroponically and my plants are aprox 1 week old. I am growing 3 plants at the moment.
2 of the plants are fine...but the third has some brown spots forming on the leaves.
It can not bee Nute burn because I have not added any nutes to the water yet, I test the PH daily and it is always at 5.7 - 5.8, My lights are far from the plants (Aerogarden will not allow me to add lights close enough to burn). My lights are on a 18/6 schedule., and also the room has perfect temperature....and I have a bubbler in the tank for co2.

My thoughts were maybe i SHOULD start adding the nutes?

Anyone have any ideas what the prob might be? I have read a lot of threads on here with the same problem...but most of them where for older plants when they were already receiving nutes..so i am kinda stumped.

Pictures below. (Best my cam will take)

I got those same spots. Not sure what they are, everyone told me nute burn because people around here apparently want your plant to show deficiencies before you feed them. Interesting that you're getting them not using any.

After more research.. I think it may be Magnesium Deficiency ..saw some photos on Google and they look close to the same. How do you measure Magnesium in a hydro system?

Not sure what it is, I noticed that on a few leaves of some seeds I started in coco. It was my first time in coco and before the first true leaves showed I noticed deficiencies. I think the don't feed any nutes thing on seedlings is blown out of proportion by guys who grow in mediums that have the trace amount of nutrients seedlings need. Your little ladies will need nutrients for sure. The seed only provides enough to get your plants to their first little leaves then they will need some nutrients to keep going. Just a little dose is all they need.

Ive fed plants with just one leaf .3EC and they were fine.

I'm thinking MG also for mine.

Was this high Ph perhaps? Causing lockout of mag?