Filter Update

I am currently a teacher aid for a marine biology class at my highschool and I am currently taking care of 7 freahwater tanks. 6 of these tanks use Marineland Penguin BIO-Wheel Power Filter while my home tank has an older Tetra power filter. My tank hasn't been setup for a few years and I am currently missing the cover for it which seems problematic and not very asthetically pleasing. Plus the new BIO-Wheel feature seems very helpful with maintaining balance within the water. Axolotls seem to be more sensitive to water levels then the tropical fish and african cichlids I'm use to taking care of (this may not be true). I know a filter is not an requirement but it seems like a very helpful tool and I am quite comfortable with using one. For my tank, which is a little over 15 gallons, I am thinking of aquiring a new Marineland filter for a 20 gallon tank (model 100) and keeping my current one as an emergency back up.

Aquarium Power Filters: Marineland Penguin BIO-Wheel Aquarium Power Filters at PETCO

The filter is for a tank of 20 gallons and I am wondering if it is too powerful for my 30inX12inX12in tank.

Any advice would be greatly appreciated =] Thank You - Stone

On a quick note it is great to see that equipment for tanks are constantly being upgraded.

The 20 gallons filter is ok for a 15 gallons tank.
But if you find that your Axolotl are stressed, you could reduce the level of filtration.