Thank you all for your help on Friday. It was a very interesting discussion which gave me food for thought over the weekend.
After a few conversations over the weekend I've decided to stay fresh for the time being with a bigger tank in the pipeline. The change to marine at present requires more time than I would want to give it (not including the increased 'viewing' hours that I would like). I'm still very keen on marine and excited by what I could do with a new 250l+ tank, so maybe not too far in the future I'll re-open this thread.
thanks again!