well i got this tank last summer to aid in swapping out the gravel in my 29 gal for sand and now i use it as a whatever tank. currently i have a 6-7 inch synadontis cat ad hes geting bigger by the day. idk if i wanna keep him or not. i also have an unknown puffer and hes really friendly, had him with lots a tetras and never touched them. im looking to put something interesting and not cichlids b/c my 29 is right across the room and has cichlids. i want something different but don't know what to put in there. i need some suggestions...

20g, no cichlids... That makes it a little harder. Very popular fish cichlids. Well, a 20 kinda limits you anyway so how about a highly planted tank. Big time decoration tank with colorful plants, driftwood, cool rocks or ornaments. Maybe throw some ghost shrimp in for fun. Or a few tetras... platys. They might eat your ghost shrimp though so careful there.