I have a terrarium of Red-Devil Crabs.
The terrarium is about 70% land, 30% water. I have pea gravel underneath the Exo Terra bedding, so that it isn't touching the water. There's no airstone or filter as it's about a liter of water and is only about an inch deep. They are terrestrial crabs, so the water is only for them to molt in, and occasionally drink from.
I keep a few aquariums, so I have equipment for water changes. What I don't know is if I should change the water in the crab's terrarium about the same frequency as I would for the aquariums, or less since the crabs are never really in it. I want to keep the water fresh for them, but if there's nothing in the water to cause it to go "bad" how often should I change it?