Orange film/crud in bottom of American Standard Champion

We remodeled three bathrooms 2 years ago. The first bathroom has a Gerber toilet and in the other two we put American Standard Champion (4?). In the two A/S toilets a pale orange film forms in the bottom of the bowl. Anyone else have this same issue? Again, these toilets are 2-3 years old - installed in early 2010.

There is one kind (and probably others) of bacteria that makes an orange slime - iron reducing bacteria. this tends to form a ring at the waterline, though. Rust in the water can stain things reddish-brown, too.