I wouldn't feel comforfable with this filter in anything larger than a 10 gallon. No room for filter media and sponge is probabaly only 3.5"-4" long.

This filter was a little bit to powerful for my axolotl tank and a little bit to loud as it just barely fit under the water. I'm sure inside of a fully filled 30 or 40 gall on tank it would be perfect but inside of my half filled 20 gallon axolotl tank it just created to much current and made a little bit to much noise! So I had to buy the 160 gph filter and it is absoultely perfect!

The goldfish didn't last too long. However, this tiny filter pump kept the water clean, and was reasonably quiet.
It will transfer five gallons of water from my rainbarrel to a bucket very fast. It powered my first solar pool heater but after I added 300 feet of garden hose the water flow was a little slow. However it was still working, and still quiet. After all the abuse I've given it, this pump still works. It deserves seven stars.

I bought this filter for my 20 gallon tank after having trouble with submersible filters in the past. So far, I've had this filter for over a month. I am very pleased with the SunSun 210 Filter. Adjusting the strength of the filter flow is very helpful, and you can visibly notice the waste particles getting pulled into the tiny vents on the sides. You can pretty much place this filter however you'd like in your setup. Cleaning is easy, running the sponge underwater and rinsing the filter parts is pretty much all there is to it. It does make some noise but not aggravating enough for me to unplug it at night. I have to add that if you have small fishes or snails, make sure that they get their food because the water will stay clean.

This filter kicks ass, when I plugged it in at first is seemed very slow but there's a cap inside that sits on top of the propellor, take it off and see the difference your self! You can also use it as a wave maker too if you don't put the outtake with 8 holes