What else will be in the aquarium?? If you have plants only, you can go the "natural" route (also called Dutch style) & do without a filter. <It is also possible to go Dutch with low bioload & plants but that is for more advanced hobbyist.>
For a 5 gal
, a small HOB
like Aquaclear Mini or an internal (sponge) filter would work.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.