MrMann what i suggest you do with your umbees is try the 6mm sinking pellet to get them to make the switch since its both large and sinks like massivore and then once they switch over if they chew too much and pellet dust is extruded switch to a smaller size. My umbee pair (15.5"-13"+) eat mostly 3mm but they will also go just as nuts for 1mm as 6mm. Once they realize its food they wont care if its small or large. Also I have found that a lot of the time if the pellet is too big its hard to get fish to switch to NLS as they arent use to such dense food and when its too big its just too much work for them to get enthused over. Hope that helps