If your cartridges are raising your pressure or are infested, it means you aren't cleaning them properly. I'm no expert on them, but soaking them in Electrosol or other electric dishwasher powder is supposed to really work. I also gather that soaking them in Muriatic Acid can clean them, but again, I'm no expert.

The two main reasons to replace carts are torn media or media clogged beyond cleaning. Otherwise, you should be able to clean them. Considering what carts cost, you should investigate this.

But the cart experts should chime in here to give you better and more detailed advice.