The best cleaning agent you can use to clean tarnished metal of any kind is water softener and salt.

If you've ever seen the commercials for Tarn-x where they dip the tarnished silver in the solution and the tarnish disappears...Tarn-x is basically water softener and saline solution. Therfore making your own is a snap and super cheap.

Calgon will work but I suggest walking down the laundry aisle at the supermarket and getting the biggest, cheapest box of generic water softener in the store.

1 quart water

2 tablespoons salt

2 tablespoons water softener

I like to use warm water because it helps with dissolving more quickly...

Try this once and I swear you'll never clean your gear any other way. Once you get your items clean I suggest taking downriggin's advice and applying some sort of oily residue, 3 in 1 or WD is what i use, this will prevent the items from further tarnishing before your next trip to the river...