Oxygenating water can only be done by first removing the C02 (carbon dioxide). To do this you have to expose the surface with either air or water. The greater the exposure the more exchange you will get. If you start to get foam on the surface you have inadequate filters - all this about so called de-foamers is rubbish - you cannot bodge a filter with gadgets. Koi at 20°C need a minimum of 12-14 milligrams per litre of oxygen to power there bodily functions. This also helps with the control of ammonia and nitrites, which in turn allows sun light into the water molecules.

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