I don't get all the "can I keep this in FW" questions sometimes
If it's a saltwater/brackish fish why not keep it in brackish. Brackish tanks aren't hard to set up, and really neither are SW tanks if it's just a fish only tank, so why stress the fish trying to keep it in FW?
It can't be that expensive to set up and maintain a brackish tank compared to SW. The salinity is fairly low so you won't be using that much salt.
Sorry, wasn't trying to slight the original poster, and I'm not saying you were planning on keeping it in FW if it really does require salt. It's just that I see these "is this a fw moray?" threads all the time, and usually people try to convince themselves that morays will do just fine in FW, when it's not that hard to do a brackish tank to keep them healthy.
I'll admit morays can be tough. Mine got out of our saltwater tank and ended up in my turtle tank one day and he's just fine now (definately fixed the lid and made sure it was really tight). But I think it's kind of low for a business to acclimate SW morays to fw and try to sell them to people as fw morays. If someone wants to acclimate one themselves and risk it dying, that's their own problem. But for a business to tell people that these SW morays acclimated to fw will be just fine, that's ridiculous.