So, can you put distilled water in your fish tank? Yes, but with a big fat asterisk. Use it for top-offs only, or mix it with remineralizers. Never use it as your sole water source.
Think of it like this: you wouldn’t drink only distilled water for a month, would you? Your fish feel the same way. They want a balanced, slightly nutrient-rich cocktail, not a chemical void.
So go ahead, grab that jug. But do your fish a favor—add the good stuff back in. Your betta will forgive you, your goldfish will stop giving you the side-eye, and you’ll avoid turning your tank into a chemistry lesson gone wrong. Happy fishkeeping!