I'm still in my first year of growing, so take this comment for what it's worth.
I frequent the infirmary threads, self diagnose, then wait for the pros to chime in, to see how close I am.
In my experience stunted growth, when all else is dialed in, seems to be a watering issue.
I have heard growers say you can't over water in one feed. I disagree. Over, or under watering has stunted plants for me, until I found the "perfect" amount for each stage in growth.
Example:
I have given small plants,15-20 days, too much(1liter). It would take more than a week to dry. Tap root never seemed to reach the bottom quick enough. Ultimately stunting growth, waiting for the bottom to dry out.
I have underwatered, feeding 250ml everyday. This seemed to prohibit tap root from reaching the bottom as well. Results were stunted growth.
In summary, I have found feeding the correct amount at the right stage of growth to be the key.
I don't see many commenting about watering habits. Could this possibly be the cause for slow growth here. Sure, more light would be very helpful, but I have seen decent results with fluorescent lighting.
To the OP, for my own curiousity, can you explain your feeding habits thus far?