The tank is essentially dedicated to the 2 dwarf puffers that live in it. There are also a bunch of Ramshorns/MTS and some yellow shrimp that live in the tank, but those are mainly there for the puffers to snack on.
So, the puffers like good filtration but they are pretty small and with live plants, shrimp, and snails the tank seems to stay very clean/stable with the little internal filter I got with the Ebi. Everyone is healthy.
An Eheim 2213 seems like it would be incredible overkill in this little tank
Even the internal filter that came with the tank causes too much flow in the tank - it's windy in there!
I am looking at some HOB filters, too, and they might to the trick. But, I can't take off the glass top (curious cats) so I would probably need to make a cutaway in the glass top to fit one.
The puffers seem to like things pretty warm in the tank. They are more mellow, have nicer colors, and seem happy at around 80 degrees and since my house isn't air conditioned and it's hot in the summers, I try to run my tanks on the warm side rather than the cool side. 78 or 80 would be fine.
For cosmetic purposes, what I really want is to get everything out of the tank. I would love to find an little canister filter that is easy to deal with and would fit underneath, then some heater that was either super discreet, could build into the filter, something like that. But, tricky to find the right setup!