The bacteria in the filter start to die off the moment the flow of water is stopped going through the media. The bacteria need a large ammount of oxygen to be able to funtion (hence the idea of bio wheels and wet/dry systems where oxygen can be absorbed form the air to allow more bacteria to form), switching filters off for longer than 10 to 15 minutes is not recomended and any time longer than this can result in the tank being poisoned.
10-15 minutes? blimey that quickly, whenever I water change or clean the filter is off for longer than that.....might have to re-think on how i do things
