Two years ago we had a new dock and deck made at our house in the Keys replacing one that was constructed with PT lumber. This time we used a product called TanDeck, a product made entirely from recycled HDPE which is largely old milk jugs. 50 year warranty.
So far it's great and still looks like new. Always hated the way PT lumber warped, cracked, splintered and weathered in the intense FL sun.