Huh. It sound like a bog. Swamps have woody plants.

If you had any idea what you were doing, you probably wouldn't have asked that. :)

I don't get how it is trickling down from the pond into the tub, and down back into the pond. That's physically impossible!

If the tub is filled with peat and sand, then saturated with water, that is a bog. You can put in bog plants.

Is it full sun?

Your correct, I dont have any idea of what I am doing, that is why I am asking. My Bio filter is part of the waterfall, I just have a small hose sifening from there down to the tub. The tub overflows into a smaller pool and then trickles back into the pond via a small creek. Maybe what I have created is more of a marsh. The water is continualy flowing through it, so it works as a filtration as well as the bio filter. I am just wanting to figure what plants might be the best to put in it, and thinking I should put a layer of sand on top of the peat mixture. Some of the peat floats.

You should go to a local native plant nursery. Ask for what kind of a plant you want. Try email or visiting in person.

Here is a link that might be useful: Native Plant Nursery Directory.

There's lots of stuff that loves wet peat/sand mix, especially in full sun - cranberries if you're in the north, blueberries, sarracenia pitcher plants, sundews, cardinal flowers, swamp milkweed (great for attracting monarchs), bottle gentians, jewelweed (Impatiens capensis -along with cardinal flower, good hummingbird attracting flowers).

There's also sedges, which may not be the most dramatic plants, but are appreciated by some bird species.

My application is similar to that described: I have a fish tank/pond and want to develop a bog filter for it. The bog will be in a dry sink 8' x 2' x 6". The question is what soil mix to use.