How long does salt last in water fish tanks?

Salt does not "last" in a water fish tank in the same way that food spoils. It doesn't break down or expire. However, the salt concentration in the tank will decrease over time due to:

* Water changes: When you replace some of the tank water with fresh water, you're removing some of the salt.

* Evaporation: As water evaporates, the salt concentration increases slightly. To compensate, you should add fresh water, which dilutes the salt concentration back down.

* Filtration: Some filters can remove trace amounts of salt, but this is usually negligible.

How long does it take for the salt concentration to decrease significantly?

This depends on a few factors:

* Initial salt concentration: A higher initial salt concentration will take longer to decrease significantly.

* Frequency of water changes: More frequent water changes will lead to a faster decrease in salt concentration.

* Evaporation rate: Higher evaporation rates will result in faster concentration changes (both increases and decreases due to added fresh water).

General Guidelines:

* For freshwater tanks, salt is typically used for short-term treatments. It's generally not recommended for long-term use.

* For saltwater tanks, you should regularly test the salinity and add salt as needed to maintain the desired level.

Important Note: Always follow the specific instructions for the salt product you're using.

It's best to monitor your tank's water parameters regularly, including salinity, and adjust your salt levels accordingly to maintain a healthy environment for your fish.