That's weird. If it was algae, i would imagine it would only come from the water source aka the faucet. Do you have the recipe for the water bowl? Maybe return it and buy a different brand although like i said, i use 2 of the extra large Zoo Med Repti rock water bowls and they are fine. If you cant exchange them, then definitely look into the Chlorhexadine. Then soak the bowl in a bucket of properly diluted Chlorhexadine for a couple days and try again. That's really weird though with your water bowl lol. Although honestly if that bowl is the only thing that gets the weird gunk, i would just return it and tell the guy that there is some weird stuff growing in the bowl whenever you add water to it.