Winter Spawning in Hawaii

Hey folks - growing red, black, golden and mottled (koilapia) tilapia here.  They love warm water!

Water temperature in tanks can reach lows around 70f in the early mornings here in winter.  I would like to encourage spawning in my quarantined fish (3 females/ 1 male).  Should I be putting a heater on that tank?  They just want to go dormant this time of year.  I want them to think it is time to spawn year round!

Anyone know mean daily temperature for optimal breeding?  I was thinking at least 78f.