Welcome to AA, DaAvid!
Let's see if we can help you out. I googled the Dynaflo 1 and found out that it is a Hagen filter. Here is a link to Hagen's website http://www.hagen.com/
. I'm sure you can find out where to get replacement cartridges. They make the popular AquaClear line - I would call and ask if any Aquaclear cartridges will fit your Dynaflo.
Unfortunately, without a cartridge, the filter is simply moving water around the tank, without filtering anything. For now, I would bring the three goldfish back - they're not going to live long without a filter anyway - unless you can remove and replace at least 1/3 of the water every day.
Tap water is perfectly fine for most fish. People don't leave the water out to age anymore - they add a few drops of water conditioner, a chemical that will instantly neutralize chlorine. You should get a bottle ASAP
. people have their brand preferences, but as long as it removes chlorine AND chloramines, it's OK.
What you need to do first is get an operational filter running and use it to cycle the tank. It's pretty well-explained here: http://faq.thekrib.com/begin-cycling.html
I Don't want to give you too much stuff to look up at once. Good luck and check back.