Sponge filter/air pump question

[zlk718]

I have a 21g long I'm using a medium size sponge filter on. The aquatop ap50 I use it with is too loud so I want to find another option. Will I get enough air using 1 nano air pump instead of the ap50 or should l use 2 nanos with 2 smaller sponges? It's a moderately planted tank, no CO2. No fish in it yet but planning for bioload to be relatively small (small school of neons, maybe a Betta and/or shrimp/snails).

[Guppysnail]

In my 20 longs I find 2 spaced out gives surface agitation throughout the tank fairly well.  The nano pumps are enough air to run a medium I have used them with the medium. Hope that helps.