I do run a 400w 6500K Iwasaki but it's over a 110 gallon stock tank so by scale, you could do much less. I had some luck running NO T12's (6 of them) over that sump and it wasn't too much/fast growth, but did grow. When I put that halide over it, it's been making a 5 gallon bucket full about every 2-3 weeks.
If you are going pc type bulb route, at least get that 65w LOA 6500K fixture. It's about 20-30 bucks and then a bulb is 15 which you need to change every 6 months. PC bulbs are extremely weak after 6 months. I may get disagreement but even the ones for the displays are dim compared to new ones after 6 months.
Flow is very important and for the sump volume look for 20-30X turnover. Shake and pull at it every day or at least a couple times a week.
I also add iron but very unregular about that. I think that may be more important if you are limited by phosphates or nitrates. I have nitrates but low phosphate. Salifert says 0 but I'm sure a better test would show more. But close enough.