nutrient temps too cold...need advice

hey guys need sum advice. i currently grow 6 plants in a tray 120 x 60cm. i have a res outside my grow room which delivers nutes to the tray using an aquavalve, but the problem im having is that the nutrients sit in the tray and when i check the nutrient temp in the tray its in the 50s.

i have a water heater in my res but not sure what to do to keep the nutrients in the tray in optimal temperature. any ideas ???

btw i grow in coco using airdomes in every pot and have air stones in the res aswell.

got some pics the heater should be fine tho

make it feed so that it only feeds when it needs it so it will take up the nutes when there warm lol i think

yeah, an aquarium heater..or two is all you need.

i have a heater in my res but the cold temps are currently lowering the temp of the actual grow room and tray of nutrients that the pots sit in. i fink il have to do what gaztoth suggested and just let nutes through when the pots are light. cnt get a pic at the moment sorry. i was thinking of buying a rootit heat mat (40cm x 120cm) with a thermostat but its pricey at £60 for the mat and £35 for the thermostat.

hope this helps a lil lol

a reptile heat mat on a timer??$$$