Thanks for that link to "Nutrient Solution Temperature is Important", Daisy. Very informative.
@Highcold, I grew lettuce hydroponically in my cellar this past winter. I had the opposite problem...too cold. The air temp in the cellar stays about 45-48, so I put an aquarium heater with a thermostat in my reservoir to keep the water temperature at 70. Lettuce did very well.
I imagine it would be tougher to cool down your system and keep it consistently in the 68-72 range. Might be easier to use other methods to keep the entire greenhouse cooler as Henderman has suggested.
BTW...when you have a chance, please post some pics of your setup. I would love to see them.
