Welcome to MFK Wazza, I don't know if I would risk an aro outdoors because even an 18" fish is subject to predation or theft, an aquaintance had several large mirror carp stolen from her small pond a couple years ago and another had koi poisoned when someone dumped bubble bath in his pond. If that isn't a problem then you can reduce the risk of losses due to fish jumping out by using an inground pond and having the ground gently slope towards the pond for several feet around it.wazza said:am interested in putting my 18in silver in 5000lt pond with the koi but dont want to loose him with jumping