50 l (12 gal
) tank is not that big, so I am not sure how much mileage you will get with just upping the size of your filter. Generally, a wet/dry filter with a sump is the easiest way to increase the circulating volume of your tank. This is easier to DIY than a canister since it is not pressurized & doesn't need to be totally sealed. However, most people have sumps for much larger tanks. <Although a standard HOB
filter can be thought of as a tiny above tank sump ...>
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.