The best way to know for sure? Grab a simple water testing kit for your tank. They cost about the same as a small pizza. You’ll test for pH, ammonia, and hardness. It takes two minutes and makes you feel like a mad scientist—but the cuddly kind.
If your numbers look good after adding treated tap water, pour yourself a glass of that purified water and relax. Your fish are happy, your tank is stable, and you’re officially a fish parent who knows their stuff. No PhD required.