Question about Hystrix

[stingray23]

I do water changes twice a week, feeding mainly prawn & krill, before i do water changes I feed blackworms, nightcrawlers & ghost shrimp. I always have the best interest of heart wwhen it comes to my fish, they are not bony & well fed. I amoving n march & planning on building an indoor pond they normally use for large koi, havent really given much thought tas to what can accomodate my aros with, but I get the feeling I am going to rehome one of them