If you are going to spend money to upgrade a decking from pressure treated to an alternative such as Composite or Plastic, consider this; most composite decking and plastic decking has limited warranties. Only one I am aware of has a commercial warranty which is Timber Tech. None of these products have been around long enough to be time tested, and some of the more recognized prouducts seem to have ongoing litigation due to one issue after another.
Ipe is my upgrade of choice. Ipe is a So. American hardwood (tabiebuia) and is proven to last 80 years without mold, cracking, cupping, warping, splintering, checking, or decay. It has oils in it which make it naturally resistant to rot and insect infestation.
Folks, I have been in the deck and dock business since 1980 in Florida. There is no such thing as maintenance free. Oh yes, some decking products require less maintenance than others and certainly the composites and plastics require less maintenance than pressure treated wood decking. Ipe does not require any maintenance "unless" you wish Ipe to maintain its original appearance. If not sealed with one of several products on the market designed for sealing So. American hardwoods. Ipe will turn silver/grey which represents oxidization on the surface. Pressure cleaning will bring the original color right back.
Ipe is a very dense hardwood and requires good skills and professional tools to install it correctly. I highly recommend you use a reputable deck or marine contractor to complete your installation. There is another up side to using Ipe. Framing for most composites and plastic deckings require
support every 16". A piece of 1" x 6" Ipe will span 30" with no support. 5/4" x 6" Ipe will span 48" with no support.
If you just have to have a composite deck, Timber Tech is my product of choice. Crane Plastics, the parent company has been in business since 1946.