What kind of bedding do you have them on? Alot of times it will be a RI due to the bedding if it is real dusty. I use Aspen bedding for my rats and mice and I rarely have a problem. Any time mine start that I use Tetracycline for birds. Its a powder you put in the water for a few days and it clears it right up. I also use it anytime I get a new one. It has always worked for me. Hope this helps.