3 Week Old Plants

i started them in peat blocks then put them into solo cups , they look healthy and have strong main stems and seem happy but i amd getting brown tips and edges on my lower leaves, growing under two ufo's in a 2ftx3ft6 in by5 ft grow tent with a fan,a 4 in exhaust that goes on every hour for 15 minutes, should i be concerned. i do not have photos, thanks

The first leaves that come out of the soil turn brown/yellow and fall off when the plant doesn't need them anymore they are the leaves with the rounded edge not jagged.

Why are you running your exhaust for only 15 mins out of every hour? What are your temps at I keep my fans running the whole time my lights are on and they shut off with my lights. I am not 100% sure but I believe you want the air constantly recirculating inside the box.

Good luck

ya i would keep the fans on all the time unless using co2