We have a Whisper HOB
Filter on the 10 gallon and a Top Fin HOB
Filter on the 20 gallon. The 5 gallon I believe also has a Whisper. They were all purchased with the aquariums, and I know they aren't the top of the line, but now that we are about $500 into this "hobby" that started with 2 free goldfish, I am a bit over budget for fishy type supplies.
The next purchase will be a sponge type filter for both the 10 and 20 gallon. The 10 will be soon, though, because the filter we have is having some issues filtering through the divider for the bettas. One side seems to stay sort of still, while the side with the filter is moving fairly well. So, I know I need a better filter on them.
I just want to be sure I am changing the filters properly. I've finally got my tanks cycled and I just don't want to have to deal with dead fishies because now the filter is all gunked up!