every one does different amounts at different times. the rule of thumb is change forty percent of your water a month whether it be 40% once a month 20% every two weeks or 10% every week wich is what I do keeps on top of things better and I do my other types of cleaning those days. Actually my friend has started doing 1% everyday he says cuts back on dosing idk that's too much for me lol. ill stick to every week