small acid and wet feet loving plant?

So I've got an aquaponics system that is just slightly to high of pH.  I also have a problem with toads jumping into my 300 gallon rubbermaid pond and not being able to get back out.  My idea was to build a floating island out of peat moss.  The acid peat moss should lower the water pH a tad and give toads a place to crawl up onto and out of the pond.

So, any ideas for any small plants that love acid soil and having water logged roots?  The pond gets partial shade.  Only a couple or three hours of direct sun.

Perhaps Bog Rosemary (Andromeda).  It likes moist acidic soil, naturally grows in bogs.  It is NOT edible!

Is this one too big?  It's edible:  http://www.pfaf.org/user/plant.aspx?latinname=Houttuynia+cordata

lots of Vacciniums would fit the bill.  cranberries?

I've got a swampy, slightly acidic, low-sunlight area, and the most useful plant that volunteers there is Prunella vulgaris.

you might also try water lilies or lotus, flags, marsh marigolds, etc..you can get floating and water plant catalogs free in the mail..i have Lilypons and a few others..just google water lilies and there will be a whole bunch that come up free, they don't just carry water lilies

Cranberries!