How often are you changing the cartridges? You only need to change HOB filter cartridges when they are completely falling apart. Just clean them by swishing them around in dechlorinated water after a water change. I've had most of mine for more than a year.
Go to lowes and buy a bag of lava rock and the coarse pond pump sponge. put the lava rock in your filter without the cartridge and add the sponge on top. Alternatively you can put the sponge around your HOB intake and pick up some polyfil pillow stuffing.
This will increase your filter capability and it drops your maintenance cost to almost zero.
I use polyfill (from a craft store) for my mechanical media, and I change this whenever it gets dirty. I also use micron felt pads (bought in bulk from Drs. Foster & Smith) that get changed every few months. For my biological media (never gets changed), I used no-brand ceramic rings I bought in bulk from Amazon.
Pinkyfilters.com! A roll is ten bucks. Cut to size. I also use the poly fill for clear water. Some bio balls, or ceramic rings and a little mesh bag is good. Anyone would benefit from taking a look at your filter and how it handles water, and being creative from there. I have even hot rodded my Top Finall in one nano tank by being a little creative with media Never be a slave to the people selling you those cartridges again.
Pinky is 2 stage and much cheaper. Price does not always equal quality. Also, what the different ply are is important. The finer side can come in all sorts of coarseness (“fluffy” side pretty much the same I think. I like pinky because it’s an extra fine. There are blue kinds that let a lot more particles through, made to use with a poly fill or pad after that as the final polisher