Here's why:
* Aquarium salt is a specific blend of salts designed to mimic the salinity of marine environments. It is used to treat certain fish diseases, maintain the health of saltwater fish, and to create a more stable water environment.
* Epsom salt is magnesium sulfate. While it has some uses in gardening and as a bath soak, it is toxic to fish.
Using Epsom salt in an aquarium can lead to serious health issues and even death for your fish.
If you need to add salt to your aquarium, always use aquarium salt specifically formulated for this purpose.