It depends. A salt water tank away from the ocean is very unlikely to find accidental contamination from you, your home, etc that‘s compatible with it.

Cause it would be fresh water species you‘d be introducing through unwashed hands etc.

But: it used to be that virtually anything to do with salt water tanks was wild caught/collected. So any time you bought a new thing for your tank, there was a massive risk of contamination.

While fresh water stuff was usually bred in captivity, with much more focus on keeping the tanks clean. Don‘t want your breeding fish/shrimp etc to just die.

So new fish were likely far removed from the wild, and only carrying the more common parasites of captivity.

Rather than introducing lethal bacteria etc that were freshly picked up from the sea.

Since there‘s also much more salt water breeding now, the risk has kinda gone down.

Plus massive operations can test for viral/bacterial DNA in their tanks and quarantine stuff.

But it you were to just take water from a random pond or a random tide pool, the risk of introducing something bad would be about the same on average.

But any random fresh water bacteria/viruses etc likely wouldn‘t survive the halinity of a salt water tank. So a ‚seperated from sea‘ salt water tank would be harder to accidentally contaminate by using say rain water from your backyard tank.