I made the mistake of putting some in my small (1.5gallon) tank once. Current flow from my in-tank Whisper filter didn't matter. The only thing that slowed down the duckweed was lack of nitrates (and the subsequent BGA that showed up). If nitrates were up the surface would be covered (and thus current reduced) in less than a week.
72g bowfront planted, CO2, 2x - T5HO, Eheim 2213 and 2013, red tiger lotus, vals, java fern and moss, crypts, swords, mbuna tank: Yellow labs, Ps. demasoni, clown plecos, SAE's.
10g mini-reef. 16lbs LR, green mushroom, star polyps, wagon wheel polyps, purple mushroom, candycane, hammer, other zoas, CUC.