Should I add saltwater to my tropical freshwater fishtank?

guppies and tiger barbs both do well with a little salt but I wouldn't but anymore than 1 tablespoon of aquarium salt per 5 gallons. Also, you should try and get 3 more tiger barbs so they have a proper school. They are semi aggressive and have a reputation for fin nipping but in larger groups they spread the aggression out amongst themselves and your guppies fins will stay intact. good luck!