Good morning, I've changed my vacuuming routine for my 265g (7' long) tank. Previously I would vacuum 1/2 the tank and 10 days later I would vacuum the other half once per month. (Please note: My tank is very well established with filter media as old as 15 years. Too, I have a lot of filter media for beneficial bacteria purposes). For the past 3 months I have vacuumed the entire tank at one time with no ill effects to my cycle. My readings after vacuuming the entire tank at one time remain 0,0, 20. I vacuum once per month. (Oct., Nov., Dec.) When I vacuum the tank, this is all that I do. I do not rinse the filter media I have and use for beneficial bacteria purposes at the same time although I do change my filter floss and pads and activated carbon if necessary. These pads and the floss I do not depend on for beneficial bacteria purposes. I also do water changes on this tank every 7 days. It's easier on me to vacuum once a month compared to twice a month doing 1/2 of the tank at a time. Since it doesn't create any havoc with my cycle, I will continue to vacuum the entire tank at one time. Ken :;rudolph Man's work is NEVER done!