I would remove the goldfish. They serve no nutrutional value, and can often be the cause of internal parasites. Plus, they create a lot of bio-load. They also encourage predation in a fish which isn't really a huge predator. So if you ever want to add other fish he may just eat them. Dithers may work, but to be honest, i would just leave the pair in the tank alone for a while. If they haven't met before it could take time for them to bond. Feed the female lots of high quality food to condition her. Just remember to keep lots of hiding places that only the female can get in. Because although you have a male and female, you do not necessarily have a pair. This is why i started with 5 and allowed them to pair themselves. To save myself this stress. I would leave them a week or so alone. If no signs of breeding then try dithers, but not cons! Something like giant danios or larger tetra species.
