Reeflow pump/water change question?

[bkelly]

I am revamping my water change procedure and think i may have to shut down my return pump to do it. My UV is hooked to it, can UVs be left on with out flow through for say 20 min? Also anyone know if its ok to turn off a reeflow pump (Tarapon) once a week to do this ? If I drain out of my tank for water changes i think sump level would get too low to allow for proper water return if i was to leave it on, right now i had been adding and removing at the same time. 180 gal tank/55 sump, say 20% change every 2 weeks.
thanks
brent