if the fish is frantically swimming at the surface it could very well be stressed. is the geo the only other tankmate with the fish? if so, does it ever bother the SAL?
SAL's will often swim around from time to time, but there is a difference between regular cruising behavior and constantly darting out of the water (which i have observed several times with stressed SAL's). if you can differentiate between these two types of swimming with your lungfish that will help us to better advise you.
as for melafix, i would not put a ton of stock in this helping your fish as opposed to a little bit of salt, increased temp (82F) and increased frequency and volume of water changes (50% changed every other day until the fish gets better will go a long way past what meds will do for a lungfish).
keep us posted on how the fish is doing, and best of luck. they are tough fish, but in treating them, its best to give them a home with non-aggressive tankmates, and treat them with high frequency water changes.--
--solomon