I bought the 5% 100 ml gold chloride solution from Siriusmetals. So I use 4 ml where I should use 20 ml of 1% of 100 ml solution for 500 ml of colloidal gold.
On another note, I was able to make perfect colloidal gold with Saltlakemetals gold chloride premixing Karo, sodium carbonate, and gold chloride and then heating in microwave. But with SiriusMetal GC, this way of making colloidal gold ends up with turbidity. I have to heat DW with Karo first to boil and then add gold chloride, and mix the solution while dripping sodium carbonate and stirring the solution with a plastic spoon at the same time, as suggested by Kephra, doing so using Siriusmetals GC produces much darker but clear colloidal gold.