Amphetamine auto grow...1st grow ever!

This is my first grow ever...it's a plant given to me at 21 days old,by a mate that has a small tent with another plant rapidly expanding!
I have just bought a grow tent and kit so it seemed logical to 'adopt' her.
But a week later and she's showing signs of weak and brown lower leaves,traces of red in the stems and no height growth, but it is forming new stem leaves and otherwise seems Ok.....am I doing anything wrong?
Grown in a 80x80x180cm tent
250 cfl bulb ( not dual spectrum... Cool white 2700k)
Bulb sat at 5 cm away
Extractor fan
Oscillating fan
20/4 cycle
Unknown soil
1/4 nutes of K, yesterday to see if that helps
Unknown ph....till I get a tester!
Any ideas would be great..... I'm a noon!

I would get her in proper soil first brother. If not adding nutes or anything is a guess on your end as you don't even know where you began. I cannot stress enough how much good soil makes a difference. I am seeing myself switching from hydro to soil recently.

Just my $0.02
Cheers

Just spoke to the original owner.....soil is neutral, nute free with a 1/4 strength nutes added.