yeah 78 degrees is a good spot for the heater, but for some reason ANY new fish I put in my 110g always head to the heater, and thats at 80 degrees ALL the time lol I dont know why, but alot of fish head to the heater <shrug>. BUT they only do that in the tanks where the heater is in the corner, so its probably a hiding/comfort thing.
both my 10g tanks, same thing. the heater is at 78 or 80 and the fish hang out around it when first added. they will liven up :)
just keep in mind, keep up the water changes.. neons arent the hardiest thing since sliced bread ;)