I have a 720 gallon tank with Severums, silver arrowana, 2 chocolate cichlids 1 male and 1 female black diamond stingray. The aquarium has been established for 2-1/2 years. I have had the rays together for 3-1/2 years. I would like to add another female to the aquarium. I have found a13 inch for sale. What are your thoughts about adding to the aquarium?