Similar to how often you need to clean your barbell, this depends on multiple variables; local weather, chalk vs no chalk, new bar vs overly rusted bar, one bar vs 60 bars, etc. Personally, I have a garage gym w/ 3 bars, live in Alaska, and use my brush 2-3 times/week for almost a year. It's just now "slowing" down but still effective. Our partner in Tampa, FL coaches at a CrossFit gym w/ ~30 bars, they clean 1-2 times/week and, 6 months later they said they "think" the brush is wearing down but it's still effective.