A filter can be shut down the medai removed and as long as there is still moisture for the bacteria it can stay alive for months as it maultiplys others die off so the new as a new food sorce again and this will keep going on till the medai is compleatly dryed out and the bacteria in a bottle as added protiens and nitrate's for it to live off and as it dies it to becomes a food sorce but as koi master said it only has a limited amount of time as it also requires oxygen i hope this helps you to understand how it works
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Hi im Dan and im addicted to Koi | 
