Thanks!I'm not sure what you will find when you test the water with 'fish-less' cycle.. did you put ammonia in the water to start the cycle?
Where are you located? South Africa? What's the coldest temperature there? I'm asking because a lot of tropical doesn't really need a heater in a milder climate. I had guppies live and breeding like crazy at the 23 C tank for a few years. I even had them outside through summer and put them back in the beginning of winter when it's 13 C out.
If you want goldfish you might be able to have only a few without it being too much on your system. They are very dirty so you might have to clean your pond way more often then if you have 15 guppies or other smaller fish.
I want to see your water fall.
Wait a few weeks before introducing the fish. But if you have to, put in 1 goldfish first (or a few guppies or other smaller fish), then add another after a few weeks. That will help start up the bacterial cycle for you.
Re test, yes, I've put in Nutrafin Cycle which apparently helps to setup the biological cycle (don't want to advertise it, don't know if it all works, yet). Of course, the guys from the fish shop were eager to sell me all kind of 'necessary' stuff.
The climate around Cape Town is sub-tropical; it can be quite cold in winter below 10C, but it's an inside pond, so the temperature variance should be fairly low. Guppys need 23-27 C? I would also prefer these fishes to goldfish...