Salt to freshwater

I guess depends on what ur goin to switch to ...I've done it a few Times I just drained 100% of water left the crushed coral in there rinsed it alil bit filled it up w freashwater switched filter media decorated how I wanted let it run 4 to 5 days put my African cichlids in ....the last time I did this I put 5 fish in there almost 2 years ago and still have them 5 fish and plus more.....

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You still need to run a new nitrogen cycle.
Bacteria's different.

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^ yep still need a good cycle. If tank has lots of deposits on the inside I'd wash them out a bit.

If the tank is encrusted with stuff - dried salt, coraline algae, ect, then yes, water and vinegar helps. I'd probably do that on any used tank regardless if it was used for fresh or salt. That way I know for sure I'm starting clean.