I'd smack the people who 'made' you install it in the first place, and make them cough up a list of acceptable plants! not to give you one at the onset is really bloody unfair of them, actually.

water hyacinth is a surface plant with a bad reputation that is ideally suited for water treatment- it traps all sorts of stuff in the bulb at the base of it. but I would check if it's legal in your area, since it's about as popular as kudzu in the south.

there are also some species of bamboo that will take the conditions, and also function as natural filters. but I don't know any species names.

when I get to upgrade from my 900 sq ft house with the 400 sq ft yard, I really want to put in a greywater system that uses plants as filters before it flows out to irrigate the rest of the garden- you're kind of lucky that way, you're half-way there!

some plants that you might want to use are Pickerel rush, Giant papyrus, lousiana iris, bog lilies, spider lily and dwarf papyrus. You could also use cattails but I would use decorative types like narrow leaf or dwarf. Also you could use arrowhead plant. All of these plants are available at water garden stores or on ebay. And will grow very fast. If you have any questions email me at. phal677@yahoo.com