Fast growing plants like anacharis will help suck up extra nutrients and keep the water from an algae bloom... I think bigger floating plants like water lettuce and water hyacinth (SP?) would help with that too, and filter the water some. Plus it will give your fish some shade and keep the water temps down a bit if its too high (from the sun). The only problem I would be worried about is that I know cichlids like to root around and move things, and that would be harmful to anything thats rooted on the bottom.