I own a 5.5 gallon QT tank. It's like any other tank. Has a filter, a heater, sand, and plants to make my inhabitants feel safe. The sand is a light color so I can see if their are any fecal issues. I'd put a filter on yours. I do 30-50% water changes once a week. I have fish in it right now, because I need to see if they have illnesses until they go up to my 15 gallon tank.
Since your fish isn't doing well, I'd do 15-20% water changes every other day and a huge 50% once a week.
Flame - Red and Blue Veiltail Male
Oswald - Blue Halfmoon Male