Shortly, if they are exposed to air. If they are kept under the water lever unexeposed they will survive longer. Perhaps hours?

They will repopulate after you start back up of course, but depending upon what you are doing, it may be like spring startup all over again.

Not the end of the world I suppose.

As long as you don't drain it they should easily last days if you can find a way to add oxygen flowing into the skippy through the media.

If the filter media is left standing in water, oxygen will be quickly depleated (within hours). The aerobic bacteria will begin to die off and the anaerobic bacteria will begin to grow. I was told by a koi dealer that it's actually better to drain the filter to prevent the anaerobic bacteria, or if you prefer, put an airstone at the bottom to add movement and aeration.

Thanks for the advice everyone!

-Chris

My pump turns off every night. The filter stays full of water, and if bacteria die because water isn't flowing, I have some hard working zombie nitrifiers because I never see a trace of ammonia or nitrite, and my pond is heavily stocked.

Chris

Just to let you know I had my pump off for 24hrs
over the weekend cleaned my pond left the water in my bio
filter turned it back on Sunday night checked my water
Tuesday night it was fine put my fish back in no problems.