java fern is a good adition... grows well and water conditions arn't really important...it would grow on your bogwood too if you wanted it to just by tying it to it with cotton or somthing then the roots attach themselves to it...can also e planted in gravel/sand too though
green cabomba is a nice plant too that looks good in groups...it grows quite fast in good conditions and gets tall so would make a good backgroud plant