My roomie has a koi tank... And would love some advice on how to make sure they are happy with their habitat and anything she could do better, but hasn't had much luck with koi forums due to the people generally being a bit elitist.
Right off the bat, a bigger tank is simply not an option at the moment. She has them set up in a 55 gallon, and that's the largest we could get them to allow in our apartment. She plans on getting them transferred to a pond as soon as she finds a place to put one, but right now, that just can't happen. She has a pair, both are still fairly young, I'd guess somewhere between six and eight inches in length. Double filtered, heated, fed twice daily using either flakes, pellets, frozen omnivore blocks, or a block of frozen bloodworms. They have a decent amount of plant cover as far as I can tell, a bubbler, hidey log, lights... I'm pretty ignorant about koi keeping, but it seems to me like she has things set up pretty well.
Any koi experts out there who could give her advice beyond 'bigger tank' or 'pond?' True, she's got a limited budget to work with, but she really cares for her fishies, and wants to see them thrive.