I must say those magnets hold pretty well, it was a real treat getting that one pair together and wow is that a lot of flow, I'm thinking about taking 1 of my 800gph phs with the hydor flo defuser on it off my 90 and putting it on the 120 and changing it for one of the koralias running 1 koralia 4 and 1 800pgh ph with flo defuser on each tank, just worried about over kill with having 2 of thes koralia 4s on the 120, but WOW is it great my fish love the one I have on the 120 right now (didn't want to shock the fish and corals with near doubling the flow in the tank in one night)