Can I keep Koi in this pond?

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A Canadian reader wonders whether he can keep Koi in a small pond. Jeremy Gay advises.

Q: I have been keeping fish since I was five, but never attempted a pond. I was wondering how many Koi or goldfish I would be able to keep in a 204 l pond. I recently saw some lovely platinum white Koi at my local store, and I was wondering if they might fit and survive our cold Canadian winters? 

NHAN S, VIA EMAIL

A: Jeremy advises: At 204 l, I estimate that your pond can only be in the region of about 90 x 75 x 30cm deep so it’s definitely too small for Koi and too small for goldfish too, especially in a Canadian winter as I fear it would freeze solid. The minimum I’d recommend for goldfish outside long term is 500 l, and that’s with a filter, and in the UK. 

I would rethink a pond this small and either use it as a water feature, a wildlife pond without fish or, perhaps, keep small temperate fish like White Cloud Mountain minnows in it during summer, if you could guarantee a period where the water temperature was 15°C or above, and bring them indoors again if it dropped below that. If it doesn’t get that warm then they are off the menu too, I’m afraid, even for a tiny portion of the year. If you can go bigger then goldfish may be a possibility. A pond of 120x60x75cm deep could hold goldfish and offers that all important thermal layer at the bottom if the surface freezes, yet it still has a small footprint which most people could accommodate.