What is the best product to use for removing salt from the soil?
This article will help you. It recommends Clearex Salt Leaching Solution and/or leaching with water:
Salt can be leached (carried) out of soil by large amounts of water. Make sure you water deeply each time you water your lemon tree, so that the water will carry the salt below the root zone, deeper into the soil. If you water shallowly, salts will build up near the soil surface and affect the roots. Over the course of weeks or months, the salt level should decrease. Also, if the water itself is salty, make sure it doesn't get on the leaves.
This article is written for Florida, but also applies to any salty soil: