If you want to keep stingray then go for it
, it's good to learn to keep fish that you want your tank is ok for grow out stingray I'm sure when time come you know what to do, I use to keep my first stingray5" in 4'tank keep him for 6 month after that I bought a bigger tank7'*2' and never have a problem with it same as water my only filter is overflow but I did change water and never let it too dirty, good luck and have fun with your ray