Salt estimate i use is one teaspoon per gallon for 0.1%.

I thought WorldGold always had both gf and discus. Now purely discus only? Last time i went also closed, a month ago

Like i said if got mucus n bubbles means water is bad. Need to figure out why urs go bad so fast. It may be some or all tat u mentioned, ie. over-crowded, over-feeding, or some disease also causes fish to excrude excess mucus. What filter u using? How often change water?

Happy goldfishing