Water Temperatures & Tips

Water temp being to cold stops the plants from being able to build up pressure, when plants cannot build up pressure they are not able to transport water to the leaves causing them to curl. Leaves curl because the are no longer able to cool themselves.
Water that is to warm have low oxygen level. Low oxygen in the water stops the plants stops the root pump from functioning properly.
Water temp should be between 68 degrees F and 71.6 degrees F. here is the link for reservoir heaters: http://www.simplyhydroponics.com/reservoir_heaters.htm this is the easyiest way to heat the water to the desired temp.
If your water is to hot then you can freeze a 2 liter bottle and keep putting that in the water or you can get a water chiller. heres the link to those http://www.simplyhydroponics.com/waterchillers.htm.
you can also add air pumps to the reservoir not only will it keep the water moving but the air bubbles cool the water. keep in mind waterpumps heat water up so if you have a aqua-ponic or aeroflo system ex: http://www.simplyhydroponics.com/aeroflo2L.htm the waterpump is going all the time so the water is hot. ( you usually need a water chiller with these types of systems).
Burying the reservoir in the ground half way or little more will also help keep the water cool.