Help needed from veteran growers..brown spots??

i just got up and running again seeds planted about 2 weeks im getting brown spots on my plants can anyone diagnose????

Have you been feeding them, and how are temperatures, humidity and air movement? Also soil type would be good to know. Peace

i have only been giving em water so far.
the temps are ok a bit of fluctuation but not much.
im just using cheap potting soil from tesco
i have a computer fan blowing on them
they have been looking ok til about 4 days ago then brown
you see in the pics started but only on two plants, mostly on 1

cheers for the reply

I would feed them with a very mild nute solution, although it is kinda early to need food, but I don't like the sound of cheap potting soil, so when you transplant in a couple of weeks find good soil at you local garden center. I like organic potting soil with kelp if you can find it. Add a little lime to stabilize ph and you should be ok. Speaking of ph, how is yours? You should be aiming for 6.3, 6.5. so that could be an issue also. Keep asking questions and it will be ok. Peace