Oh, don't tell me that.... I just got an AC50 and have a prefilter for it for my 20g. I have heard though that most HOB
filters will lose flow after a few months (or was it weeks) of use to a point, bit that it's completely normal.
If you want a sponge filter why not go for a Hydro 5, I have read Hydro sponge filters are the best and comparable to AC HOB
filters. I have no first hand experience with them, just read a lot of reviews. They are so cheap ($15), you might as well get the 5 (recommended for 40-125g tanks depending on the pump you use). I'm sure that would cover it fine, but you might want to consider getting 2 smaller ones because I'm not sure how big they are and if the 5 is really big it could be an eye sore