I think a tank of 40 gallons is too big for keeping licorice gouramis properly. They are not fish for swimming and they tend to hide. You will not be able to breed them, to raise the young, to feed them, even to find them (the young).
I keep them in 12 liter tanks, 20 are good, also.
In my tank there are no filters whatsoever. Filters are mainly for people who feed the usual industrial food, and this to bigger fish or many fish that produce much waste. You don’t have this problem with Paros.
The only really useful aspect of a filter for Paro-keeping is that it keeps the water moving. But mostly the water movement is to heavy. A small filter driven by air bubbles ist better than any other.
You cannot replace the regular changing of water by filtering. The waste (although it is very little in a Paro-tank) must be removed out of the water-cycle. A filter does not achieve this. It only replaces the waste from flowing freely in the water to a narrow place in the filter. But the water is always drawn through it until you remove it.
But why do you ask this in the category “species”? We have a category “methods”, for instance. We should try to keep the wohle thing clear in order to be able to find things again.