Out of curiosity, what size tanks are you using yours on and what is the fish population? I am going to guess you are not keeping fishes that produce lots of waste.
Well, you judge for yourself. I have a 400 on a 75 gallon tank with a couple black belts (12" male and 7" female), plus a pair of salvinis (4/6 inch) and a school of rainbows. I have a 280 on a 30 gallon with 8 Crypt. panamensis, 4 Thorichthys elioti, 6 Cory. panda and 6 Cory. aeneus. I have a 400 on an 80 gallon bow front with about 30 3-4 inch fish in it, and a bunch of plants. I feed fairly heavily. Maintenance is 1x per month, or when time permits.
But now that you've mentioned it, I'm not surprised you are clogging so quickly when using sponge in the filter.