Slow Veg Growth

[OregonGrown79]

So, I am on run number 3 inside. First was a photo plant, second was autos and now another photo. Both photo runs have had slow veg growth. I am on week 6 from seed and still have a 1 foot tall plant!!! Granted she has been topped and now has several more tops but she is still small in stature! I am using a 400 Mars2 and growing in FFOF. She is currently in a 1 gallon fabric pot, trying to grow some good roots, and soon will move into her new 8 gallon fabric pot. I just fed her a tiny bit of nutes the last watering so I am hoping that helps. Any ideas why my babies grow soooooo slow?
OG79

 

[Fuzzy Duck]

More likely the topping slowing things down a little & takes a bit longer to pick up with growth.

 

[The bonger]

Have you checked your ph. I had a plant just stop growing and wondered why for about 2 weeks. Tested the ph and it was coming out at 5. Flushed and fed and it took off and caught up with her sisters.