Thanks for the advice and the article. I think I will avoid getting another as the symptoms my poor fish has are exactly as described and identical to the last one we lost. I don't want to make the problem worse by supporting the trade in them. I Just hope my swordtails and rainbows haven't caught a species transferable version of it!
There are a lot of sub-standard dwarf gouramis around and a lot of them are already infected with a virus when they are shipped over. They do prefer soft, acidic water but hard water shouldn't affect them that badly. What are your water readings? What other fish do you have apart from the rainbows? If you're dead set on getting one then I would see if you could track down a breeder rather than getting a farmed one.
I have a mature tank with mostly rainbow fish in which I've had for years. They never seem to get ill. A few weeks ago I added a dwarf gourami he is now looking very drably coloured and poorly. Years ago when I had one of these fish before the same happened. Thing is I love them but I wonder if our hard water is to blame. I don't want to get another one if this is the problem as its not fair. Does anyone know if its likely to be this or if they are, perhaps, just a bit overbred and not very hardy? Water parameters fine by the way and tank not overstocked.