Thank you for your question. You may certainly switch salt mixes, however to avoid shocking the specimens in your aquarium you would want to gradually switch mixes over a period of 4-6 weeks. To do this, you would want to combine the new salt with the salt you are currently using. A good way to combine the two salt mixes would be a combination of a ¼ of a regular dose of the newer salt with a ¾ of a regular dose of the salt you are currently using. With each water change you can gradually increase the amount of new salt you are mixing and decrease the amount of salt you are currently using until you are completely out of the older salt (which again should take 4-6 weeks).
Ultimately, the type of salt you should choose should be based on personal preference; however we use Instant Ocean brand salt in our aquaculture facility and call center aquarium. Please refer to the link below to view this brand of salt and reef crystals. - mar