Any pain can be used to be honest as long as it doesnt get in the tank!I used a paint,I didnt use flat though,I use gloss,I would use it,dont get it in the tank though,thats all I have to say.
Any paint will do... No matter what you put in the back it will look shiny inside since the tank is glass or acrylic and it's shiny... If that makes sense lol...