No, aquarium salt does not lower water hardness.
Contrary to a common misconception, adding aquarium salt to your tank will not reduce the level of dissolved minerals that constitute water hardness (like calcium and magnesium).
Understanding Aquarium Salt and Water Hardness
Water hardness is determined by the concentration of specific mineral ions. Lowering hardness typically requires processes that remove these ions, such as using a water softener or performing significant water changes with softer water sources like RO (Reverse Osmosis) water.
As stated in the comments section of a relevant discussion:
Salt isn't going to lower the hardness. salt won't soften any water unless used with a water softener.
This clarifies that standard aquarium salt, which is typically sodium chloride (NaCl) or a blend of salts, does not chemically react with or remove the minerals responsible for hardness. While salt is used in some water softening systems, it serves a different purpose in those systems (regenerating the resin that captures hardness ions), it doesn't directly soften the water on its own simply by being added to the tank.
Why This Matters for Your Fish
Understanding the effect (or lack thereof) of aquarium salt on hardness is crucial for fish health.
- Different Fish, Different Needs: Many fish species have specific requirements for water hardness. Keeping a fish that needs very soft water (like some South American cichlids or tetras) in very hard water can cause stress or health problems.
- Identifying Issues: If fish are dying, and they are known to thrive in your water's hardness level, the cause is likely not related to hardness or the use of aquarium salt regarding hardness. Other factors like ammonia/nitrite/nitrate levels, pH, temperature fluctuations, or diseases are more probable culprits. As the reference suggests: "...fish also don't usually die from hard water unless its a soft water fish living in liquid rock, i would explore other possible causes of death first."
In summary, if you need to lower the hardness of your aquarium water, you should explore methods specifically designed for that purpose, rather than relying on aquarium salt.
