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Old 10-02-2012, 09:25 PM
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Doghouse Riley Doghouse Riley is offline
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First recorded activity by GardenBanter: Sep 2009
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The idea that there can be a layer of warmer water at the bottom of a pool is a myth. It won't happen in normal koi pools of around five or six feet in depth. You'd need to have something well in excess of 3 metres.
The running of filters and the movement of wish would prevent that happening if it did anyway. Deep pools will benefit from the transfer of some heat from the surrounding earth, which is always warmer than surface ground temperatures

My koi pool is five feet deep, but it has a swimming pool cover, the filter is insulated in a room in my garage and I've a small heater in the pool. I'm maintaining +6c. I wouldn't want it to go lower than that.

Many koi in their first year won't survive sustained temperatures close freezing point for long. Larger fish may, some won't, there's no hard and fast rule with koi, so best to be on the safe side.
Goldfish are a "completely different kettle of fish."
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