I have a hippo about 4” in a 65 gallon tank. Dimensions are 36x18x24. There is rock with multiple hiding spots. The top half of the tank is open so there’s a good amount of empty space. Tank mates - 3 chromis, 1 maroon lightning clown, fire fish, 2 pajama cardinals, mandarin, various snails & hermit crabs. She swims around a lot. Very active but chills at times too. The LFS will take her back. How do I know when that time is?