Well gentlemen, I have stalk and vine plants floating on foam in my sump. Judging by their root growth, leaf production, leaf size and water parameters....I would say plants in a refugarium/sump should certainly be considered.
My system houses three stingray (14.5, 12.25 and 12) inches respectfully. I am dealing with approx 390-415 gallons of water, with a turnover (filtering) rate of 7.41 times an hour.
The plants I added, and the fashion in which I added them has markedly improved my water quality. I do things a little diferent: I do water changes when the NO3 exceeds 5ppm.
Before the plants I would see this and do water changes almost every 7-9 days.
Now, with the plants, I see this and have to do a water change every 20 days or so.
*** some disclaimers ***
I am an amateur at this and these are only observations.
I do not claim to know it all.
I am not saying my set-up will work for everyone.
*** ***
Respectfully, FireMedic