I own a Aqua Fizz and my sparkling water is not fizzy enough.

Let's get this figured out :)
To carbonate using the Aqua Fizz, press the carbonating button with short, firm presses until you hear a buzz (release the button between presses). Three buzzes will produce a standard fizz; additional presses will produce a stronger drink. Never press more than 5 times or your bottle will runneth over!
If your sparkling water still isn’t fizzy enough, you may need to replace your gas cylinder. Click here to learn more on how to exchange your gas cylinder.