The oxy type cleaners are pretty effective. You can mix them up in a 5 gal pail and then use a small "broom like" scrubber. Rinse with the garden hose.
This article cover cleaning a wood deck but the oxy cleaner can be used of trex too.
OK, please understand that I know NOTHING about this deck material...
Can it be cleaned with a power washer?
My neighbor has PVC decking, and uses a power washer 2 or 3 times a year to clean it....