You need to set up a quarantine tank for your new ray. remove her from the main tank and keep her in quarantine for a month. use the same water from the tank and an established filter. do 20-30% water changes daily. keep temp at 82F or even 84F. offer foods every day for ten minutes or so then remove so as not to create any extra ammonia. if you have access to live foods you can leave them in the tank - try live black worms, live ghost shrimp, and even live fish if they are clean. keep the tank out of bright light and in a relatively quiet area. no need for salt or stress coat. I recommend using prime as a water conditioner to detoxify ammonia and chlorine. the quarantine tank does not have to be huge, maybe 60 gallons or so. bare bottom is fine. keep aeration high as well.