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.