Thanks for the advice! I went to Petsmart recently and bought a small water pump. That way the water won't be flat and stagnant - hopefully that should make water changes less frequent, right? It would just be a bit frustrating to change the water daily, because the bowl that I bought is quite large and heavy and is positioned in a specific way in the substrate.

One final question - heat pads. Necessary or not? I've seen some people recommend them but others don't. Do the tribbies seem to enjoy them?