plant not growing please help

i am growing in a dwc cabinet prebuilt flos mounted one on each side 20w 6500k 1200 lums one 600w hps munt.at top not useing hps at this time.plant is only 1 1/2 in tall about the same as it was 2 weeks ago ppm 517 ph 5.7.now i am haveing heat probloms in cabinet maybe do to heat out side.inside cabinet temp is 30 to 31c water is 26c.how can i fix both thank you ps cabinet is 3ft w 2ft d 4ft h

help somebody