What type of top decking was used?

redwood

Where do you live? What is the exposure? What do you want the deck to look like color wise?

i live in sacramento, CA. it gets full sun on the deck during the middle of the day ... there's no real shade on it! i really don't care about the color. i just want to protect the wood. what product(s) should is use, how often do i apply it.

Not sure his reasoning for putting nothing on it, I would at the very least put a clear sealer on it or a very very light colored stain. Just visit a true paint store and purchase a quality product they recommend and quality appropriate applicators. Can't help you much more as Calif. has availability issues that I am unfamiliar with as far as products.

A stain with UV protection would be a good idea, IMO. The sun can be very harsh.