Unsealed stone and concrete surfaces may also be broken by dissolved Epsom salt splashed or dripped outside the tank, because of the dried salt recrystallizing and opening up cracks and fissures. Epsom salt is not corrosive in the way sodium chloride (desk salt) is but chlorine can attack some surfaces https://directoryrecap.com/listings13046072/the-best-side-of-how-to-isolate-tanks