The water in a pond will become foul very quickly. I would suggest adding a small pump just to circulate the water under the false bottom. This will raise the humidity and keep the water from stagnating.
hey i have a "pond" type arrangement in a twenty high and it only has a water pump, (which is comlpletely buried under larger rocks) not filter, and ive never had any probs with the water. i would think the plants roots have a healthy effect by cleaning somewhat, and i was told wood would help the pH. just take some out with a turkey baster every once in a while