Dear Mainer61:
If your deck is Trex Origins boards which is the deck board that is smooth on both sides, one option is to flip the deck board.
It may be a bit darker than your current boards at first but it will weather over time to the blend and it won't have the bleach mark.
Bleach can lighten your Trex deck. To minimize the lightening affect of bleach recommend diluting the bleach with a 50:50 mix of water, especially for the darker Trex board colors. The following cleaners contain no bleach and are Eco-Friendly:
Corte-Clean Composite Deck Cleaner (
www.corteclean.com)
Chomp Pro Algae & Mildew Stain Cleaner (
www.chompsolutions.com)
If you can post a picture of your concern it may assist us further in resolving your concern.
Regards,
Pat M - Trex