At 34L you are pushing the limits of keeping many fish in there ... but I have seen two small ocellaris clowns be quite happy in 40 litres so its not far off. You would need to ensure to do regular water changes and provide proper filtration for them though, as clowns are pigs and will produce a fair bit of waste. Slack off and your tank will turn into algae central.
Check out coral gobys too - they are cute, have personality, and add practically zero bioload to your tank.