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I have an aquaponics system to provide our above ground vegetables such as lettuce, spinach, silver beet etc. I have found that over summer, even when shaded the growing media is getting too hot for the roots and the plants die off (this year, 2 weeks > 42C). I am starting to covert the 1/2 IBCs to having 100mm coarse gravel with well in middle covered with weed mat, then about 150mm sand, topped of with a mixture of soil and compost and composted chicken/cow manure.

Does anyone have any experience with wicking beds? And can they provide some guidance.

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No experience at wicking beds, but a couple alternatives:

Can you circulate the water through an evaporative cooler?

This could be as simple, as a place in the shade with a small pond and a pump that converted some of the pond to mist. The aquaponics solution remains separate, and is circulate by a separate pump.

Is the diurnal temperature swing large enough that you can cool a pond with several times the mass of your aquaponics system at night enough to keep the aquaponics water cool during the day.

The best way to do this would be to have insulated panels (roofing tin on top of strawbales) exposed to the clear night sky, set at a slightslope. Add the water on the uphill edge. It radiates skyward. Collect the water at the lower edge and return to storage. Turn off when ambient air temp becomes higher than water temp in the morning.

The Persians used to make ice this way. In a desert climate on a still night, an insulated metal tray can radiate enough heat to freeze an 1/8" layer of water into ice. This depends on very dry still air.

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