These mini filter is good product. I use it with my 18 L tank as second filter with Jebo 502.
Both of them keep my tank crystal clear.
Jebo 502 is easy maintenance, while Resun CY 20 is a good canister filter, small and reliable.

A great little filter, attached to my 15 litre (20L total volume) mini-tank. NB. I don't use bagged carbon in my canister filters, so have replaced that media with some quality filter pads instead.
Provides great filtration and surprisingly powerful flow for its size. If not for the movement of the plants, I would not know the filter was powered - absolutely silent.
Priming was mostly painless, although fiddly, but the quality of the outflow elbow pieces which go over the tank rim isn't great, are quite brittle and leaked on mine. Someone with a more delicate touch might not experience this fairly minor problem. I found it best to connect the hose directly to the vertical in-pipe to eliminate the risk of leaking.
I'd definitely buy one again without hesitation!

Very good filtering!

I use for my 112L marine tank, great filtering, almost no redslime after 7 days use! great for lps and sps to keep nitrate down.

I juse it in my refugium as a hang on particel filter and i altso gone use it in my quarantine tank.
Easy to clean,small and no noice .