I don't change my sand. I sieve mine gently every day to remove anything thats not supposed to be there and just top it up when needed. I dont have the sand in there all the time though. Just for 1 hour every evening or they wee in it
I leave mine in the cage and sieve it every day as they use it as a toilet. I do it morning and night to keep it clean. My living room looks like a beach in one corner due to sand flying out as they use it lol I use it for 3 weeks then renew it all. But everyone does different things with baths don't think their is a right or wrong just how you feel yourself.