capetsma Nano Aquarium Filter Sponge Fish Tank Filter, Ultra Quiet Sponge Filter Worked with Aquarium Air Pump, Include Spare Sponge and Bio Balls.

Easy to install, easy to operate, easy to clean. Working well in my 2.5 gallon nano tank.

I used this in a 3gal aquarium, and it works wonderfully. Super basic, no moving parts, and it's small enough for tanks even smaller than 3gal. I did put a valve on the air tubing because the air pump I used was a little too big for the small tank. Highly recommended for small tanks.

I was having problems with Algee in my 30 gallon freshwater tank. these seem to be helping. The foam filters are getting dirty and so are the little balls. the instructions said not to rinse the foam when dirty... just squeeze them in the tank?? doesn't really make sense to me. but they did send an extra set of filters so i will just replace them each time they get dirty. It took some fiddling to find the right setting between my large air stone and this filter. i turned the valve to the airstone off and then slowly turned it back on until both the filter and the airstone had air. The filter isn't super strong. i've watched flake food float right by... but again, they are getting dirty so they have to be catching some gunk.

Air leaks through the bottom. And the spare sponges doesn't even cover the length of the filter.

It's a great sponge filter that works. I didn't really need it but I like redundancy in my aquariums so that if one's of other filters fail I have back ups. I use an undergravel filter & a canister filter for my 55 gallon aquarium.