Hello, The Mayer, and welcome to TFK!
I'm guessing that if this is a newly set-up tank, the filter is not the issue at hand. Most aquariums have to go through whats known as a "cycle", also known as the "nitrogen cycle". Basically your filter needs to grow beneficial bacteria in order to handle the ammonia load which wil be present in your tank. The beneficial bacteria which needs to be grown, breaks down ammonia in your tank(which comes from fish waste, as well as food) into a far less toxic version of ammonia, ammonium.
If you are un familiar with the cycling process, please read up on this: http://www.tropicalfishkeeping.com/f...m-cycle-38617/
--For starters I would do a partial water change in your tank, 50%. Be sure you're using a water conditioner for the water going into your tank (Prime is a great one, as well as API Stress Coat).
-- I would try and get a reading of both your tap water and your current tank water. If any ammonia is present in the tank water, I would do an immediate water change. Any ammonia in your tank can kill your fish, so we need to keep all that in check. You can take your water to your LFS (local fish store) and have them test it for you, and while your there pick up an API Master Liquid Test kit. The kit will allow you test your levels at home, and be crucial during your cylcle. When you go to the LFS, have them give you exact numbers for your levels. Then post them here.
Once we have your water parameters, we can go from there.