heater for 5g?

[sabazerehi]

first i'm wondering if i even need a heater for my 5g. with just the lights on it's already at 80F, however, i don't know how low it's gonna drop at night. so should i get one? and if so, what heater is good for a 5g? thanks

 

[jpeggerling]

25 Watt Stealth