Thanks for the comments, it does look a bit empty at the top I admit, but I'm hoping some of the plants in there will grow up and fill the space, maybe I could put some floating plants in till they grow?
As this is my first attempt, wasn't sure how mad to go with the rocks so I've just put a few in initially, infact on the left hand side, I've built the green rock into a cave, but it's a bit obscured by the plant, I also toyed with the idea of driftwood, but my wife doesn't like tanks with brown water which can happen with the wood ( sounds daft but it took me a lot of work just to get her to agree to have the tank in the first place!), I believe that a carbon filter would take this out and clear the water, but it would also take other nutrients out, so I'm just not sure at the moment.
Cheers,
Keith