Thanks everyone for your much appreciated help and experienced advise. I've syphoned the offending growth along with a 20% water change this morning, but see tonight that it's returning ... so yes, a skimmer seems to be the obvious solution.
And yes, small problems in a new tank, (particularly for a novice like me) do become major issues, but with all your help, I'm now looking on them as a challenge rather than a worry.
Thanks all. I'll check out skimmers and see how I can somehow incorporate one into my tank on the weekend. I'll keep you posted.
Cheers, Ray.