I would go by smell as well. sounds like you are removing most of the poop, which could make your set up work kind of indefinitely. we have a variety of fish tanks, terrariums, reptiles, hampsters and of course birds. I've found through applying a bio-active approach in several enclosures that you just need to keep an eye and a nose on it, it can go for years being balanced and then one day, things go south and it needs a good mucking out. the two smells I look for are amonia (burning to nose and eyes) and rotting (anaerobic bacteria-> methane.) I wouldn't worry about bleaching, the "pro-biotics" usually do more to hold stuff in check over the long run than the chemicals... unless you have a major toxic bloom or infestation of some kind, then go nuclear if you have to.
