Thank you
Look hungry start feeding nutrients and cal mag.
What nutrients are you going to use.
5 weeks in ffof no nutes yet? Yeah i would feed. There hungry. If not check PH of soil
So welcome to the community.
They look very healthy my freind 
Those lower leafs are brown from touching the soil and is very common.
If the site of the really bad ones bothers you, you can just pluck them off.
As others have said, after 5 weeks in OF, is very likely the nutrients is just about used up and i would start feeding nutrients pretty soon.
Also did you mean the light is on 24hrs a day?
Its not really a problem for autos, but you do have some light stress going on with the leafs “tacoing” up on the edges. I would suggest simply going to a 18/6 light schedule.
I run 24hr lights for the first month or so myself, then I switch to 18/6.
But over all they look good to me 
Set light to 18/6 and give them a good feeding next time they need watered, and if you are not giving cal-mag yet, give cal-mag water between every feeding and I think you be surprised at how they respond…
How many plants r in the same little trays of dirt there. 5 weeks with more than 1 plant in each tray would prolly be starving if food as the plants all most likely ate the nutes already being cranked together. If that’s how it is how it looks atleast. One plant per pot or they will likely fight in the root zone for who is getting what food at what time. One or more night suffer from lack of something.
Suggest using a PPM meter to determine when to feed. Runoff PPM ~1,000 is the time to start feeding a balanced cannabis product.
Don’t worry about yellowing of lower leaves. It is normal for them to yellow and fall off as the plants mature.
You will struggle to flower that many plants in a 3x3. More plants doesn’t necessarily mean more yield in a space that small. One or 2 healthy plants will yield good results.
Whoaaa… 8 in a 3x3 ? that is gonna be one hell of a challenge in flower. Hopefully you have a lot of fans because that’s gonna really choke the air flow. I generally only run 4 in a 5x5 and space is a challenge at times.
Good luck to you, you really have your hands full.
