They work Great. We have been using them for about 8 years, and think they are real workhorses. We have two planted freshwater tanks, and run two sponge filters with powerheads in each one. The 20 gallon High tank we have two powerheads with fine sponge filters and that is it. The 55 gallon we run a Eheim 2215 with a corse pre-filter sponge filter and a double stacked fine sponge filter on a single powerhead. The reason to run two sets of sponges is when you need to clean them, you just clean one then about 3 or 4 weeks later you clean the other one. This way you always have a good supply of bacteria growing in one or the other. And if you need to set up a tank quickly, you can move one of the filter into that tank with some of the gravel and water from an established tank and you have a new tank set up with lots of good bacteria. Check this site out. They have lots of great stuff and tons of sponge filters. I use the hydro II and hydro III sponges.
Hope this helps with some of the sponge filter questions.
Roy:o)
Edit: Roy, thanks for your help, but I have a general policy against posting commercial links in the forum. Hence, the link has been deleted. Mustafa
Sorry about that.
How about if I mention that Jemco is a great place to get sponge filters?
Thanks,
Roy:o)