I would go with the Aqueon 30 myself. That's what I use on most of my tanks. I just rinse the cartridge out once a week and replace it once a month. You can get a 12 pack of cartridges on Amazon for $22 so you are talking about $2 a month for cartridge costs.
chickenlady, do your clamshell holders go all the way to the bottom? There is a key feature on the bottom of the filter that the cartridge and holster slide into. If your clamshell holders do not go around this key feature the cartridge will not go all the way to the bottom and water can bypass under the cartridge and back into the tank unfiltered.
Thought you should know.
Andy
chickenlady, do your clamshell holders go all the way to the bottom? There is a key feature on the bottom of the filter that the cartridge and holster slide into. If your clamshell holders do not go around this key feature the cartridge will not go all the way to the bottom and water can bypass under the cartridge and back into the tank unfiltered.
Thought you should know.
Andy