Really depends on what type you are talking about...Florida ricordea can handle and do very well under med flow, while Yumas will stay small and possibly not open at all under med/high flow.....I have a bunch of Ricordea Florida that are in med/high flow and are doing great and opening very well but it is not direct flow, but bouncing off the glass and back at them in an intermittent pattern due to a natural wave timer....