sumps help manage top off, increase water volume ect.
But, they do increase the cost of the tank.
Almost everyone who keeps reefs ends up having them eventually and never go back once they do.
40gal is a nano though and borders on should I or should I not.
Lots of us here have the equivalent of 40gal nano but use a 100g sump for it.
A sump bigger than the tank is an obvious boon to filtration.
anyhow.... you need to provide WAY more information if you want a suitable response.
