Tiger larvae not interested in bottom of tank?

[SarahFaye]

I have two tiger salamander lavae in a ten gallon tank and they swim swim swim. Neither seem interested in exploring the bottom of the tank, unless it's to swim through the holes in the artificial tree stump. Is this normal for tiger larvae? The water is about 6-7 inches deep and when they're not swimming, they're hanging out near the surface. They seem happy, and I know tigers are aquatic in the larval form, but I don't know...should they be more interested in the bottom of the tank? Especially since there are ghost shrimp down there for them to munch on that they don't seem too interested in.

 

[Linus]

How long have you had them?
What are you feeding besides ghost shrimp?
Do they appear to be having difficulty coming to rest on the bottom?