these are your minimums:
3000 lumens per sq ft in veg
5000 lumens per sq ft in flower
if you have 24 sq ft then you need 72,000 lumens minimum for veg, and 120,000 lumens for flowering
so 2 400 watt mh bulbs will net you around 70k total lumens
and 2 400 watt hps bulbs will get you around 100k total lumens
you seem to be just below your threshold. what i'd suggest is section off the space to 4X4 or 4X5 at the most.
as for your grow itself. at 4 weeks your plants should be larger then they are. the fact that you have been under feeding them is probably the biggest reason they are as small as they are at the moment. also you need to find a larger medium to plant them in immediately. you can put the rockwool in a large tote full of soil. or place them in a net pot and do a dwc hydro setup. when properly fed for a few weeks those roots will be bursting out of those blocks.
if you plan on using rockwool in the future make sure you soak the rockwool in properly ph'd water before putting them to use.
and get a ph pen & ppm meter asap
