Can I grow on Koi in this set-up?

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One of our readers would like to get some Koi to grown on in their tank, with a view to transferring them to a pond, Jeremy Gay gives his advice on the best way to do this...

Q) I would like to buy half a dozen 8-10cm Koi to grow on in a 450 l aquarium, with a view to transferring them to my pond, which will be finished next summer. I have a secondhand FX4 filter I could use. Would this be up to the job with messy Koi and what filter media would I be best to fill it with? How should I furnish the tank, as I presume plants will be dug up. Please can you advise?

NICK B., VIA EMAIL

A) JEREMY GAY REPLIES: The FX series of filters are probably the most capable on the market when it comes to messy fish, so it’s a good choice for young Koi in an aquarium. They do come with the right media, but all you’ll need is a good amount of ceramic biological media to take care of the ammonia conversion, and sponges or filter floss to do the mechanical side of things. You may want to add some carbon periodically as I find coldwater fish like goldfish and Koi can create quite a smell when kept indoors.

Koi will grow quickly so change water regularly and add an airstone to provide oxygen for both fish and filter bacteria.

You could grow them on in a totally bare tank, but if you want to decorate it, use fine, round gravel, which they will sift through, and maybe a piece of wood and some smooth stones. Go for plastic plants, tough, waxy live plants like Anubias, or no plants at all. The fish won’t be bothered. Even a tank of that size will stunt their growth eventually however, so do make sure they go into the pond as soon as possible, so that they can reach their maximum growth potential.