Are they visible or invisible? (From your descriptions, it seems you can see them. If not, how do you know they are hatching eggs?)
You need a BNC to positive and negative aligator clips cable (http://atelierrobin.net/images/aligator.jpg).
My FG isn't the one on ebay, but they are similar. Select Square Wave. Hook the cable to the TTL/CMOS output and use the TTL/CMOS knob to control current output. (You can also hook the cable to the 50 ohm output, but in that case you should turn the offset knob to max or close to max. Someone told me it is better to use the TTL/CMOS output and I follow the advice.) My FG doesn't have the Duty knob and you have to experiment with the knob.
You should zap as frequent as you can. I zap over 10 hours a day (fortunate that I have retired and can do whatever I want at home).
An idea just came to me a few days ago: If I use both TTL/CMOS and 50 ohm outputs (I will have at least 4 contact pieces in that case), I may get increased electric current. I have ordered an extra BNC to positive and negative aligator clips cable and am waiting for its arrival.
How did you get the mite infestation? [I am clueless about it. I got it when the weather started to get warm and humid April last year. It seems more and more people are have this issue. Maybe someone (govt.?) is spreading the mites.)