I clean once a week or as otherwise needed. Use your nose! Lean in and smell..........good? or like socks? Humidity causes dampness, which causes odors to run free.......
Mine took a dump one night last week, and even though I had just cleaned it the day before, the smell wouldn't go away so I had to clean the whole thing again......
I use a very weak bleach solution and then rinse over and over and over again. They have ultra mega smell sense (as I'm sure you know :wink: ) and I feel it's important to really get the bleach back outta there after cleaning.
The bark I'm assuming you just pitch whatever is soiled and add new as needed. I use astroturf, which I wash and then dry. I made two pieces so I can dry one and use the other.