alot of buckets. U do need a large portion of the tank to be filled with the water it orginated from. Then slowly replace orginal water with fresh. Probably take 2-3 weeks to fully adjust but it can be done. That's actually how i started with natives. But I had to keep mine somewhat brackish because I was planning to add a tailor to it, which didn't end up happening
depending on size, some lfs sell bream and flathead that were farmed and raised in freshwater. So the hard work is done. The trick is knowing who actually has them. Also, its wise to look around because their prices can vary immensely.