Here’s your cheat sheet: fill the tank halfway, use water-softener-specific salt, and check it monthly. If your water is suddenly hard, add a bag. If it’s still hard, you might have a bigger problem (like a broken valve, which requires a plumber and possibly a small sacrifice to the appliance gods).
Remember: salt is cheap; replacing a water softener is not. So go ahead, toss in a bag or two. Your hair will thank you, your dishwasher will stop plotting against you, and you’ll have one less reason to feel like an adulting failure. Now go pour that salt—but not too much. You’re not a salt factory.