The Hagen A1394 is the correct replacement insert for the following filters:
The Hagen AquaClear A1394 Foam Insert - 3 Pack is a set of replacement aquarium filter inserts for the Aquaclear 50 and 200 Power Filters. This three pack of foam filter inserts traps particles and debris and is tailored fit to prevent bypass. The Aquaclear A-1394 is compatible with 20 to 50 gallon aquariums.
Hagen AquaClear A1394 Foam Insert - 3 Pack specifications: