Recommendations for mold/mildew additives for deck stain???

My white cedar deck is under some very large oak trees. Even though I've scrubbed, bleached, washed and restained this deck, by this time every year the surface is black.
This year I'm planning on belt sanding down the entire desk to get to the wood and applying some type of protectant be it tinted or clear sealer. I'd like to add a fungicide to the material to hopefully reduce some of this black stuff longer into the season.
Does anyone have any recommendations for such an additive available at home stores? All suggestions welcomed other than cutting down the oaks.
Thanks
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BobMCT wrote:

Time was, there were a number of things. Many had copper - which made the wood green - but others used metals/chemicals that imparted no color. Unfortunately, our government has decreed that they are a no-no.
One can make a home brew borate mixture of ethylene/propylene glycol with borax and boric acid. They are quite good but are water soluble so no good for a unprotected wood like a deck.
Your best bet IMO is to buy a commercial product with a wood preservative already in it. Readily available at Lowes, HD, Ace, paint stores, etc... http://www.google.com/#hl=en&sugexp=les%3B&gs_nf=1&gs_mss ck%20fung&pqck%20fungicide&cp=8&gs_id?&xhr=t&q=wood+preservative&pf=p&sclient=psy-ab&oq=wood+pre&gs_l=&pbx=1&bav=on.2,or.r_gc.r_pw.&fp81970977896a9f&biw3&bihI9
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dadiOH
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On 8/20/2012 10:57 AM, BobMCT wrote:

I doubt that it will matter what you finish the wood with, as the conditions are perfect for mold. Consider having the trees thinned/lifted so that the area gets more sunlight.
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The deck sounds like it is being stained by the tannin in the oak debris... Since tannin stains everything, wood, concrete, asphalt, roof shingles, etc there is little you can add to any stain or paint which will prevent that...
Decide which is more important, the shade provided by the tree canopy or having a perfectly clean deck which is the color you want it to be...
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What is black, the wood or the stain?
Did you try oxyclean ? Add 3-4 tablespoons per gallon, spray, dry, repeat.
Greg
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