I loved mine on my 5.5. I now have a 6 or 7 gallon (can't remember and haven't cared to figure it out) and even that little difference has seemed reduce the flow in the tank quite a bit. However, it has been vary reliable for about 4-5 years. Super quiet as well. I don't know if I would buy one again, I would look into Finnex or a 511 instead.