What Temperature For Koi Fish Tank Is Appropriate? It is well known that koi fish are very hardy. It has been talked about again and again that koi fish are able to handle a lot of different water conditions and can easily bounce back from illnesses and other issues.  This is part of what makes them so appealing for such a wide range of fish hobbyists, they are easy to handle and can generally live for decades, making them a fantastic pet for children to grow with. Still, sometimes they get sick and need a little help.  This is where quarantine