I have used salt on all my amazon catfish with no ill-effect on the catfish what-so-ever. In fact they always heal much faster stay free of desiese and grow faster than they ever did before I used salt. Granted you don't want brackish conditions, but a lil salt works wonders. To answer your questions the feeler (aka) barbells, or whiskers are an appendage of the maxillae in whichs is housed thousands of nerve endings and taste buds. Each one has more taste buds than an entire human tongue. They do grow back and this can go quickly or slowly depending on your tank's water parameters. Melafix has always seemed to help mine heal quickly. If you do use salt and heat treatment ensure that you have extra aireation in the water because it can be harder for difused oxygen to be asorbed through the gills. I would suggest a salt treatment over medication any day. It is a more natural treatment, and all bodys of freshwater have salt in them to some degree or another. A general rule of thumb is to use 1 tbsp per 5 gals of water. Slowly increase the salinity of your tanks over time and once you hit this mark keep your tanks their always and you'll notice more healthy and desiese free fish. Only use evaporated sea salt, never iodized salt, because it contains iodine which can be lethal to fish, esp scaless fish. I've had catfish loss whiskers and when they start to grow back you will notice the end of the injury will for a round or ball like end. Then a tiny whisker that looks out of place will start to grow out from there. Usually takes 5 days to about 2 weeks for them to grow back completely. I would also make that larger tank a priority. 100 gals is kinda small for a 20" rtc. Might wish to cut back on feedings a bit until you can get a bigger tank. This will help with water quality, and I would suggest 2 %50 water changes per week until the barbell is completly healed!