Hi Giz !
First I have to apologize for giving you wrong info!
The distance between the silver wire must be 3cm (I read in one page), 5cm (I read another page). So I say 3-5 cm
(but NOT 5-7 cm.. ).
About the candle part... just put the glass/porcellaine pot you are producing the CS-Water in on a candle so that it gets heated from the bottom. The hot water will slowly circulate. It's just for optimzing the process, you can also leave it out and use a spoon to manually achieve that.
The voltage must be 27V. 3x9V (your zapper) = 27 Volt. I guess your zapper is somehow trippling the battery voltage to get the 27V when you use it for CS production.
You can test it easily: After a maximum of 30 minutes you should see the water becoming yellow (good) or gray (bad). If just nothing happens, then there's sth wrong.
Guess you wont need that, but here is a diagram how it looks like:
Let me know if you suceed..