Thanks, Greg. I'll have a go with just straight Luminance and see how that goes. I was hoping to capture some of the fine detail from the Ha and that's why I tried blending with the Lum as well.
David, yes, it is a bit strong
I realised that the whole image was quite dark and have stretched it a bit more. I think the my-little-pony colour is tamed a little by this:
http://rickstevenson.smugmug.com/Astro-Photography/2012-07/24276295_KctMFz#!i=1988539736&k=ZRJ ZDnz&lb=1&s=O
Cheers,
Rick.