Hello and welcome to FF! Sorry for your froggie tragedy . First of all stop feeding calci-worms (Hermetia illucens); they are extremely hard to digest, and not the best food for a recovering frog. Gut loaded crickets sized same as distance between eyes or earthworms are a better food. If the salt treatment was working and you can get frogs to eat; would continue that until they get better.

Having frogs in the wild is a bit different from having them in a controlled environment. One of the things would check is describing pond, material it's made off, and include a picture if possible. Then would need to discuss the water, type, and if you tested it's pH, ammonia, and nitrite levels.

What made you think frogs had Chytrid fungus? What symptoms where frogs exhibiting? IMO common frogs are not more susceptible to pathogens than exotics. Any frog can be exposed to pathogens and depending on it's immune system it can handle (or not) a number of pathogens. Stress the frog out or if environment gives the upper hand to pathogen... and both the common or exotic frogs will be in trouble .

If you want to keep an exotic frog (and being frog fans we want all humans to do so) will need to sterilize any enclosures and materials, decor, etc. that where in contact with the sick frogs. Need to research what frog to keep: Frog Forum - Choosing a Frog. Then once you decide, read the appropriate care article and set-up an enclosure that meets the frogs needs. When you get your frogs, quarantine them for 30 days minimum with 2 negative fecals 2 weeks apart and that will get you started correctly with your new frog pet/s. Good luck !