Fish poop makes ammonia. Ammonia is very very deadly for fish. Bacteria in the filter turn ammonia into nitrite. Nitrite is pretty deadly for fish too. More bacteria turn nitrite into nitrAte. NitrAte is bad too, and needs to be removed with regular water changes, because there are no bacteria that eat it.
chloramine is chlorine mixed with ammonia. It's bad for fish. You get rid of it by using chlorine remover, which you can buy at any fish store.
there is a bacteria that feeds on nitrAte, however, they live in oxygen depleted water, so it does not live in our aquarium(s). There are special setups that you can purchase or make yourself; however I'm not very familiar with them.
I use a sink filter, one of those purifier thing that's used to filter out the chemicals for human drinking purposes. They last a loooong time and I highly recomend it.