If you're into goldfish - that's cool. Stick with it. You may get into tropicals later, but some people do not. It sounds to me like you are doing everything to the best of your ability.
Your tank is small, and therefore a little harder to keep stable than a larger tank. But if that is all you can afford, stick with it. It suits your fish for the time being.
I look after a goldfish tank for my daughters kindy. It has 2 fancies in it, and is quite similar to your tank. All I do is a 40% vacuum and water change, once a week, with water straight out of the tap. The fish are in good health. They will out grow that tank in time, but at the end of the year they'll move to another home anyway when the kindy year ends.
Blackmoores, I have found, are a little weak - perhaps not an ideal first fish. But stick with it - and yep, perhaps joining the club in Dunedin will help.