My tank is 2 x 1 x 1.5 ft, got a 2 ft pl light (not sure how many watt). The tank is pretty new, not much plants, the lights can get to the bottom.
I use inserted 10 lumps of the box of 'super root monster' fertilizer.
I also drop CO2 tablets once a week.
btw, my tetras, SAE and otos are living well after 2 months, but ALL of the cherry shrimps are dead the following day after i put them in! *sigh*