The AC sponges will last for
years, no need to constantly replace them.
Here's how my AC 500's (110's) are set up. One big sponge, two layers of fine blue/white media sandwiched together, then a thin double layer of polyester media for the very fine particles, topped off with a bag of bio-max rings. My water stays crystal clear.
The bio-max ring bags alone have enough bacteria in them to keep the tank stable after cleaning all other filter media. There are far less costly bio media items available than bio-max rings, but I scored these at an auction for next to nothing, and they have performed very well for me over the years. I also never replace the bio-rings, I simply lightly rinse them in clean dechlorinated water when cleaning the other filter media. Contrary to what Hagen states, they too will last for many years.
HTH