If you are going to get one, you are better to convert it to salt water or keep in heavy brackish water. In freshwater they will produce more waste than most systems can handle and will probably die in less than a year.
These rays are designed for saltwater, but due to their unique renal function, they can live in freshwater. However, being in freshwater makes them create 10x the amount of urine, which in the wild isn't a big deal because of strong water flow and natural filtration. But in captivity, it builds up in the confined space and takes a strong filtration system + frequent water changes to manage. Making the water brackish (partly salty) cuts down on the urine production, but still requires a lot of filtration. I've had mine for a few weeks and had to double the filtration I had (2 filters at 500 gph each, totalling 1000gph on a 125g tank), and even with 2 water changes per week I'm looking at an even bigger canister filter right now because it just isn't enough to keep the levels below what I would like. Not to mention that these guys eat raw seafood, and that adds to the amount of ammonia and nitrates in the water. I did weeks of research before bringing mine home, and used those weeks to get the tank cycling and 100% perfect before putting my girl in it. I suggest you do the same, because you don't want to take any risks with such a delicate (and expensive) animal. If you want to put in the time and the work though, they are worth it.
Here's the thread I've had going here since I started up, it has a ton of useful info from more experienced ray keepers and also what I've been learning as I've been going along.
good info u got there PinkLady ...
i had one, and i kept up the water changes.... it did fine, at a lot of shrimp ...
but i had to move it to another tank one time, and mysteriously passed away ( water was fine in both tank ) , so ya.... beware when they change environment... they might not adapt
He'll be in a 180 gallon tank thats running over 1800 gallons per hour and I'll be doing as many water changes as necessary. He should be fine. In all honesty I would rather have a south american ray but Florida law says I cant.
180 won't be enough water volume to offset the waste it will produce. Just keep it as saltwater, it's much cheaper and better for the animal in the long run.