To add a liquid, do everything as you would for adding a custom salt, check the Liquid checkbox which opens a new field. Density is discovered by dividing the weight in grams (kg) by volume in ml. Both of these measurements are on the front label, on the bottom. 1 liter of 0ppm water weighs 1 kilogram, so if the contents weigh 1.1kg, there's an extra 100 grams in the bottle. 1100 grams / 1000ml = Density. I think you need to set the Concentration Type to A or B, but I had no issues when combining salts with liquids when playing around with various things.
I had difficulty tracking down the contents of AN, so good luck.