Usually one is all that is used in a tank, however, if your tanks needs higher flow there are many attachments for the spray bar that can extend your return flow.
I loved my ehiem canister spray bar when I had my 90 set up as a reef tank. But it was horrible for the seahorse set up. By limiting the return flow, the water "sprays" out of the tiny holes in the bar at a much higher velocity. Which causes great water flow for reef tanks, but Valiant did not like the high flow rate from it at all.