10% every week and still haveing trouble getting nitrates to 0!!!
I do what changes whenever I get around to them, probably every month or two now. If I had more time I guess I would do them every month, on a set schedule, around 20%.
I dose vodka and mb7 (based on the experience of SunnyX, who previously posted) so I basically only use WC's to replenish trace elements that I cannot dose myself. I do 5G every couple weeks.
+1 but mine tank is only 50gal.