I usually add a little salt when I prepare water for betta fish. Salt can reduce stress of betta fish and increase ion to tap water. The best ratio when you add salt to water for betta fish is 1 ppm - 3 ppt. (1 ppt = 1 g / 1 liter of water and 1 ppm = 1g / 1 ton of water)
Salt also reduce disease growing rate. Betta fish live in a backwater so it is great if you add a little salt into it. Salt can protect them from disease.
When I send fish to my customer who live in other countries , I never forget to add a little salt into betta fish's water.
Yeah!!!! SALT REDUCE BETTA FISH' S STRESS. HALFMOON SPECIES WILL BITE THEIR FIN IF THEY ARE VERY STRESS!!!!