Can I get some Koi for this pond?

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A reader asks about acquiring Koi for a mature pond with existing fish.

The house I’ve bought has a pond in the garden, built by the previous owner five years ago. It looks very natural, with loads of plants in it. It’s constructed using a liner and there’s a filter system hidden in a little shed which keeps the water crystal clear. I asked the previous owner a bit about it, and he said it holds in the region of 11,250 l. In spring most years there is frog spawn and tadpoles, and I’ve also seen a newt.

But the issue is that I don't see the fish much. Even when I feed them, I have to sit and wait five minutes before they come up, quickly grab the food and then disappear. The previous owner says there are about 40 fish in there — a mix of standard goldfish and Orfe.

Would I be able to add some small Koi once the weather warms up? The house I rented prior to buying this one had a pond with Koi which were so tame I used to hand feed them. 

TRISH, VIA EMAIL

Jeremy says: Yes, you could add six 15cm Koi to a pond of that size and they will grow to about 60cm long in a few years. Their ravenous appetites and tame personas will mean that they'll be first to the food while also tempting the other fish out to feed as well. I suspect that with such a mature pond, some of the existing fish may have been born in there and have reverted to a more wild existence, especially with abundant natural foods. Feed at the same time every day, but you may also need to consider thinning out some of the other fish as the Koi grow. 

The potential downside to adding Koi is that they may well dig, causing water clarity issues, so you could need a larger filter in time. Koi may also eat tadpoles, some plant life, and make the pond generally less inviting to frogs, newts, and other wildlife, especially once they start getting large.