Species only 20 gallon?

[SlugSnorter]

hello. You could do a squid, however sea horses would be a great unique animal to home.

cephalopods are a big challenge. they need special care. and this tank is pretty small too

 

[SlugSnorter]

you could perhaps get an octopus.

bad idea, they are very demanding and need special care

 

[SlugSnorter]

you could have a nem or RFA garden tank filled with nem dwelling inverts.

 

[majesticbigmac]

Try browsing the nano fish section on Live Aquaria.
Most popular small fishes would be clowns, but you have lots of options.


For real?

Yes. I have kept a dumpling squid in a 25g, however their lifespan is short lived.