New cedar deck has mildew - need advice

My husband and I have spent the last four weeks rebuilding our deck. We decided to go with a cedar surface because we love the natural reddish colour of the wood.
We nailed the last board in on Sunday evening. Everything was perfect - straight, flat, lovely golden/rosy tone.
There was a thunderstorm on Sunday during the night. On Monday morning, we awoke to discover that our lovely new deck has developed mildew. In the space of EIGHT hours. I kid you not. Many of the boards are speckled with little black marks, and the top stair tread has a big grey mouldy looking stain. It's bloody awful.
Is this normal?!? The guy at the hardware store seemed really surprised that mildew would develop so quickly. What makes it more perplexing is the fact that the deck is south facing, and has been baking in 30 degree sunshine during the construction process. We live in a dry climate with very low humidity. How the hell does mildew develop in that?!
We had hoped to lightly buff the surface with a sander, then finish off with a natural coloured UV protection oil. What we're worried about now - how long do we have to wait after cleaning out the mildew, and will the mildew grow back before we get a chance to sand and stain?!? I would have thought no, but I also didn't think that mildew could appear in the space of a single night.
Were we supposed to treat the boards with the protective oil on all sides before we nailed them down?
Also, I've noticed that some of the boards are developing hairline cracks. Is this normal for cedar?
We thought we had everything in hand, but the appearance of the mildew has really thrown us off course. I'm beginning to wonder if we haven't just thrown a huge amount of money down the drain :-(.
Gillian
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I'd suggest calling in a mold remediation specialist and having the spores tested at once.
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"Ranieri" <uh-uh> wrote in message

That seems a bit extreme for mildew appearing on some decking. I know it happened overnight, but even still...
Are you saying we have something serious to worry about?
The deck that was in place when we bought the house was badly built and too small, which is why we're rebuilding, but there wasn't a hint of mould on it anywhere.
Gillian
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Nah, my comment was tongue-in cheek, mold hysteria being what it is. As Ed said, give it a wash with a mild mildecide (Jomax works well) and see if it returns.
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The wood may have been contaminated before you ever saw it. Use a weak bleach solution to get rid of it and I'd use Penofin oil to protect it.
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If it had been contaminated before we got it, would it have been visible? We checked the wood carefully when it was delivered to make sure there were no bad warps, gouges or other damage. It all looked great.
Gillian
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Did you use a microscope to find the mold spores?
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