The specs say for aquariums up to 125 gallons. I assume your correct w/ flowrate. Like I just said I run that as precaution against power outages. I was running two HOB units & the sponge and a few weeks ago disconnected one of HOB's as the three filters were a bit overkill for the stocking level I have currently.
The main reason I went with the sponge was for bio filter and based some of my decision off of this guys research and actual real world testing/experience.
truly with decent flow, ur substrate and plant roots will house much of the bacteria in ur tank
the sponge is good for a power outage,
keep lighting simple to keep it low tech, that's a MAJOR factor as light drives the need for everything else in the plant world
also with low stocking such as you have, tank will be easy to maintain and will require less frequent water changes.
just watch for overfeeding, that's more damaging to water quality, than a fish that eats all the food, and utilizes it.
decaying food is horrible for water quality