What telescope refractor aperture size would I need to observe Mars's polar caps? I have a Levenuhk Strike NG 80mm, and I can see red disk of planet but cannot see any details on the surface.
According to this website, you may actually have a big enough refractor to see them, but only on a "good viewing" night, and when Mars is close (opposition):
4-6" reflectors or 3" refractors: polar caps, large surface features
This website also says that 80mm to 90mm will let you see the Martian polar caps:
Martian polar caps and major dark surface features during oppositions
I hope that helps. Your 80mm should work, although it seems to be at the lower end of requirements. You may just need better atmospheric conditions. Clearsky is a good website to check out.