Your frog is not an "African Marine Frog", he/she is a African Dwarf Frog. They must be fed thawed (and ONLY thawed) bloodworms nightly and should be fasted one day a week. They need 2-2.5 gallons of water PER frog and do best with temperatures around 76-77*F. They are VERY sensitive to water conditions and most medications are toxic, as is salt.
I have a 20g species tank of them myself and they are about 3 years old now.
The fish forum I moderate on is one of the leading sites for help with African Dwarf Frogs (ADFs) and I highly suggest it - http://p076.ezboard.com/bflippersnfins
They are a species that needs very specific care. They breath air, so it's vital they have space at the top of the tank and they are amazing escape artists and they die VERY quickly once out of water, so your tank needs to be totally free of ANY openings. They are 100% aquatic and they are not that smart so you need to plug any places in decorations with filter sponge so they cannot get stuck. They are also nocturnal.
Here are a couple photos of some of mine -
This is a male practising amplexus - he's not positioned quite right but he's trying -
Here they are hunting -
They cannot be kept with fish that are greedy eaters because they take a while to hunt for their dinner and they need to have gravel that is large enough that they cannot swallow it -
Oh and they are nearly blind - like Mr. Magoo - they can only see what is about 6 inches in front of them, if that.