We have just had our builder lay a new forest redgum deck and over the first night it was layed we got a shower of rain. The decking had leached out a very black and ugly tanin (not mould as it has only been down for less than a day).
Just after some advice of how to correctly clean and treat the wood to get it back to the lovely colour it was yesterday so we can oil it.
Thank you so much for sharing pictures of your new deck. The stains you're looking at are the result of a chemical reaction when tannins, water and iron particles mix together. The iron particles could have been picked up from anywhere from the processing plant to the chains that held the timber bundle together.
The best way to counteract this staining is to use oxalic acid. A good oxalic based cleaner is Feast Watson 1L Woodclean, it will convert the stain into a different compound that is colourless. Feast Watson Woodclean will aid in the removal of oils, mould, stains and tannins from new and weathered timber. It's Ideal for rejuvenating grey, weathered timber, Woodclean is suitable for restoring decking, outdoor furniture, fences, pergolas and other exterior woodwork.
Please note that Feast Watson Woodclean is a powerful cleaner and is used prior to oiling your deck. It will remove any oils or tannins that are currently on your deck. I recommend testing an offcut of your decking timber before you commit the entire deck.