Did you clean the filter media in tank water or in tap? Did you replace all filter media at same time? If either of those questions answers is yes; you accidentally wiped out the filter's ammonia/nitrite reducing bacteria and it's biological capabilities. It will take up to a month for system to recover and in the meantime, your frog is exposed to toxic ammonia/nitrite and might be suffering from it.

If the above is an issue; treating with meds will only provide temporary relief until ammonia/nitrite levels are zero again. You can test water for ammonia/nitrites if have kits or take a water sample in clean bag to local pet shop; most will test for free. If either is present tell us the results and start doing 25% daily water changes until levels reach zero. Then you can resume weekly 25% water changes and clean the filter media in tank water removed during water change.

A bit of salt as stated is OK for treating minor infections. Myself have not used Maroxy and I'm not even sure if it's still available. Mardel was bought by large pet conglomerate and many of it's great products (i.e. Maracyn Plus) where discontinued. Stress coat is not going to eliminate an ongoing pathogen attack and the binders in it can actually harm your frog.

My recommendation is to take care of ammonia/nitrite issue if required. Get at pet shop's aquarium section some Melafix and Pimafix. You can use both treatments at the same time. Mix them according to label directions and treat your frog for a week. Hope this helps and keep us informed of frog progress, good luck !