It's likely not clear because your tank isn't cycled
New filter in a new tank means you need to cycle the tank.
Basically, the nitrogen cycle takes place in your filter, this is where bacteria consume the toxic waste of your fish and leave the byproduct nitrate which is removed via water changes.
Head to the getting started section and read up on Fish-In Cycing since you already have your fish.
Do you have a test kit?
Daily testing and water changes may be needed to keep him safe till the tank cycles.