Most of the articles I read and the advice I got from that guy that keeps them is that they do better in brackish than freshwater, due to the urine output like you mentioned, and that is what my plan is. Right now I have a 125g tank with a 300g filter and can easily add a second to double the rate of filtration if needed. She is about 8" wide right now so when she gets bigger, I will be upgrading to a larger tank as we'll have moved to our new house by then and I will have the lower level available. I don't plan to have any tankmates for her other than a few guppies hanging out in the top levels until she eats them, so not really any increased bio-load other than the ray herself. It will cycle for 3 weeks before she comes home to ensure I can get the levels right -- chlorine and nitrate are at 0, nitrite is still hovering at 10-15 but the tank has only been up for 2 days so there isn't much balance in it yet. I did add a Nitra-Sorb pouch to the filter and was thinking about getting CaribSea sand, although I'm not sure if it's meant for anything other than saltwater? Alkalinity is at 8.0 but that should come down a bit more over time as well. My only concern is the water hardness, as my landlord doesn't have a water softener for my house. Hardness is over 300ppm, maxing out the test. Are there aquarium water softeners available? I did read 2 articles that said Atlantics can handle harder water than you would think, that they adjust and do just fine. But she would need the ability gradually get used to it through routine partial water changes, so until then I need to be able to make it softer in the beginning.
Has anyone been tagged by one of these rays? The one I have on hold has a full tail but her barb has been removed, although I do know they often grow back. She is very active, docile, and eats very well, she actually took a few pieces of food from the manager's hand, so I have hopes this is something I could continue doing with her. Overall I just think it's a gorgeous ray and will be really awesome to watch, especially for my 3-year-old.