[Versa12]

Prestone green coolant is fine.

if it's only down a bit, i just top off with water, but not too much or it'll be too diluted. i've never ever flushed coolant. never been a problem in thirty years of driving

If you are topping off with water make sure to have a bubble coolant gauge to see exactly how much protection the coolant is offering.

In my experience at my old job, Dex Cool become super nasty and sludgey if it never was flushed. Its not a bad idea to get coolant flushed every so often!