Is there a product I can buy at Home Depot or Lowe's that can be applied to metal pipes coming off a tub drain that can prevent or slow down corrosion?

I have two tubs, one had a leak and had to be replaced with a portion of the metal piping. For the second tub, there is no leak but there is a little green and white stain or corrosion on some of the piping. I can't afford to replace that tub and piping currently so I wanted to see if there's something to apply to extend the life of the piping for now.

Here's a pic:
https://docs.google.com/open?id=0B6F...FZNQm8zY2VGdGs

Based on the cast iron tub, brass and copper fittings and the growth rings on the joist, this tub has been here a while. It looks like some solder flux corrosion. Get some steel wool and try to wipe it off. You are lucky to have lasted this long without needing replacement.