Bubbles bubbles everywhere

I have a thing for bubbles.  I love carbonated water, carbonated wine, carbonated beer, etc etc.  We were spending mucho dinero on topo chico, the most delicious mexican fizzy water you've ever tasted.  But buying and drinking fizzy water by the case gets pricey and also leaves a lot of empty glass bottles to be recycled.  Enter the sodastream.  I've known about them for years, but the price tag was a turn off.  Recently they've come out with tons of models that are less expensive, certainly still pricey, but less than half the $200 they once were. So, off to bed bath and beyond with my 20% off coupon and now I am a proud owner of a sodastream.  It is awesome.  Aside from the actual satisfaction of carbonating something, it tastes great, especially with a wedge of lime squeezed in, and it is so darn easy!  I don't know when the break even point will be but overall I am very pleased.  I only wish I could carbonate other things, such as cocktails with it.  But that would void the warranty and possibly break my new beloved gadget!  Soooooooo, enter the iSi soda siphon!
I splurged and bought one of those specifically to try to carbonate cocktails.  There is a system made for that purpose, called the Perlini.  As $250 a pop, plus CO2 cartridges, I figured I would try the less expensive approach first to see if I even liked a carbonated cocktail.
My first attempt was a carbonated Negroni.  I put the empty siphon bottle in the freezer overnight, then put in 1:1:1 ratio of gin, sweet vermouth and campari to fill probably half the bottle.  I shook it, put in one cartridge intially and tested.  It came out super fizzy but the fizz waned quickly.  It tasted basically like a Negroni.  I added another cartridge and tried again, still, the same thing.  I then placed it in the freezer for some time, and then the fridge.  Always the drink came out super fizzy but then lost its fizz quickly.  Good news is it kept for almost 2 weeks in the fridge, bad news is I haven't dialed in the carbonation quite right.  But a still Negroni is better than no Negroni!

Next stop is carbonated aviation station....I have filled the iSi siphon with gin, lemon, violette and Luxardo.....we shall see if the bubbles work better this time around.....