Martin - would you let the fast growing plants just float too? I have a large tank that is like a jungle and my new tank is tiny? such an obvious suggestion I hadnt thought of it!Fast growing 'real' under water plants will help for sure. They should be cheap and you can also use simple plants from a pond. Just let them float, this also helps to dim the light a little.
Thanks - now got half an acre of cambombia floating in my tank