Water pumps are crucial to adequate water flow in marine aquariums. Because of this, it is very important to keep them running in tip top shape. Regardless of which make and model pumps you use, they will become less efficient over time as algae and other crud gets stuck on the impeller/propeller, intakes get clogged, and impeller shafts get bent or broken. The unfortunate thing behind this is that there is no real way to gauge if your pulp is working optimally, other than by going off visual cues. That is why it is important to perform consistent routine maintenance on each and every pump in your arsenal. Remove them for service, break down individual components, give them a good vinegar bath, scrub everything to remove the gunk and grime, reassemble, and out back into service. This is the bare minimum you should be doing, and while the frequencies may vary, the maintenance should be performed at least every few months.