I had a treated deck built 6 years ago, and the floor is already decaying. The wood is very dry and brittle and can be pushed through when some force is applied. I have applied sealer stain/water sealer twice over the 6 years. My question is, "What in the world could have happened?" Everyone else's deck lasts for years and years. Could it have just been bad lumber. What are some tips in selecting lumber when I replace it?