How long can I turn my filter pump off for? Never is the short answer, a filtration system needs to run 24 x 7 for most beneficial results. Filtration pumps should not be turned off or placed on a timer. Why you ask, here's the science, nothing complicated but worth knowing. Inside your filter there are beneficial aerobic bacteria colonies. This beneficial bacteria do the work of converting the ammonia produced by your fish into nitrites and then into nitrates. As your fish need oxygen, food and minerals to survive so to do this aerobic bacteria in your filter box. It is estimated that this bacteria can die of in as little as 4 hours. They grow back but putting your pond through this constant cycle of death and rebirth is hard on the ponds ecosystem and causes poor water quality. Even if the bacteria don't die, each time you turn of your pump they start to go anaerobic. So when the pumps is turned back on the resultant surge of water though your filter washes out debris into the pond often with the accompanying smell. So it is best to leave your filter pump running permanently and only turning off for brief moments of necessary cleaning.