There are several reasons stains, marks & discolouration appear on your deck.
We'll go over a few of the common problems and see what can be done about them.
1: Tannin Stains
What is Tannin?
Tannin is an natural organic preservative produced in many plants & trees to help deter predators, with some species having a higher tannin content then others. And yep, it's the same stuff that stains your teacups and gives your a red wine a dry mouth...
After a few months, you might notice the colour of your oiled deck starting to fade a little and the finish looking less lustrous. This is normal natural weathering and nothing to be concerned about - just your deck responding to being exposed to the elements.
Every six to twelve months is the right time to make a little effort on maintenance.
You've made an investment in quality timber, but...