In my experience, Gouldian finches are more susceptible to illnesses caused by poor environmental hygiene than other species of finches. I have noticed a direct correlation between the health status of my flock and the level of hygiene in their environment. I clean perches once per day, I change water twice daily and replace ground cover as needed to maintain a minimum of fecal buildup. In addition, I make sure to clean out nest boxes a few times before the chicks fledge, when the parents will allow this. It really does make a difference!
As a daily disinfectant I use Nutribiotic grapefruit seed extract (GSE) at six drops per ounce of soapy water and simply place this on a wet towel or scrubber. GSE can be found in health food stores. It works as a substitute for bleach in terms of killing germs but is a non-toxic cleanser that is entirely safe to use around birds.