Looking at the improved colouration of the guppies, they playful behaviour and the happiness of the corys after being moved to a tank of this size, I am slowly coming to the conclusion that smaller tanks are really a stressful place for most fish to be.
I added 6 small gold laser corys yesterday. They are no bigger than some of my younger guppy males. So far so good although I got them via post. I didn't quarantine them so I need to be lucky for once. Hope all will be well.