I made a borax crystal rock Can o pout it in my fish tank for decor or is gonna desolve?

Borax crystals should not be placed in a fish tank as they can be harmful to fish. Borax is a water-soluble compound and will dissolve over time, releasing boron into the water. Depending on the concentration, boron can be toxic to fish, affecting their gills and causing difficulty breathing.

Furthermore, borax can alter the water's pH level and create an alkaline environment, which is not suitable for most fish species. The recommended pH range for most tropical fish is between 6.5 and 7.5, and introducing borax may raise the pH beyond these optimal levels.

To ensure the well-being of your fish, it's best to avoid using borax crystals or any other chemical compounds not specifically designed for aquarium use as part of your tank's decor.