I put a C3 on my 29 gallon on August 26. To date, my water has been pristine ... crysal clear ... and polished.
Then yesterday (September 26) ... boom ... the little red warning indicator pops up telling me the Poly/Fiber pad is clogged/clogging and needs service. I have a foam pre-filter so the coarse side of the pad wasn't bad but the ultra fine portion (maybe 100 microns??) was udderly clogged with debris.
I rinsed and squeezed it vigourously in distilled water and a ton of dirt came out but the pad still looked quite dirty. I put the pad back in and noticed when I started the filter back up, the little red warning indicator would not go back down. I was not too worried because I'd seen that before in product reviews where people claim to re-use them a couple times before replacing even though the red indicator pops back up.
Well ........ a couple hours later ........ the water was still reasonably clear but had lost all of its crystal clarity and the "polished" look.
So I replaced the pad with a new one and sure enough ... the little red warning indicator went back down indicating the flow was back to normal. I seeded the new pad with part of the old one but probably did not need to since I have a pre-filter and my carbon compartment has floss and Purigen).... and of course I have the bio-max stuff that really never needs changing.
Here is a link to my album with a picture of the side by side comparion of the "old" pad (after cleaning) and the new.
Aquarium Advice - Aquarium Forum Community - Paul1792's Album: Paul1792's 29 gallon - Picture
Bottom line: The "fine" portion of the pad gets so packed with micro-debris that it cannot be effectivelly cleaned and re-used.
The bad news here is losing all the beneficial bacteria from the pad unless you seed the new one. I don't mind the $1.50 a month to replace it .... but I may do some custom cutting of my 100 micron polishing pad I use for the aqua-tech in the other tank together with another foam media cut to fit that can be rinsed and re-used while throwing the polishing pad away each month.