I'd also say that it's probably not worth doing, in your case. That said, here is some general info on how this can be done. More specific questions are easier to answer, though.
Sounds like you're unsure of all of the math involved, so unsure of what to buy to increase nicotine level in your zero nic liquids, while maintaining a certain PG/VG ratio. This is one of the most complex problems, here, and asked about fairly often.
Many use calculators to do the math for them, but not all are geared toward remixing existing
e-liquids. I've heard that this one can do so, and it's popular:
eJuice Me Up - Best eJuice Calculator
I don't use anything but a generic calculator, so I'm not sure what these e-liquid calculators can do.
General info:
To increase the nic concentration of a liquid, you'll have to have an e-liquid that's at least a bit higher in concentration than what your target is.
If you are trying to get 10ml of liquid from zero to 6mg/ml, and you are using 8mg/ml to do so, you'd have to add 30ml of the 8mg/ml to the 10ml of 0mg/ml to get 6mg/ml:
10ml of 0mg/ml + 30ml of 8mg/ml = 40ml of 6mg/ml
One way to calculate that is like so:
(0mg + 240mg ) / 40 ml = 6mg/ml
That is just adding the total nicotine
content in mg, and dividing it by the total volume (ml). That's how we get mg/ml, which is the nicotine
concentration. Figure the total mg nic by multiplying the mg/ml by the ml.
The above example is not very efficient, and results in having to enlarge the batch by four times. The higher the mg/ml nic that you add, the less that it will require. For example, you'd only need to add about 1.11ml of 60mg/ml to 10ml of zero nic to get 6mg/ml:
10ml of 0mg/ml + 1.11ml of 60mg/ml = 66.6mg of nic in 11.11ml of liquid, so 66.6mg/11.11ml = 5.995mg/ml
Assuming that you would be using flavorless nicotine liquid to enhance flavored e-liquid, the first example dilutes the original flavor to 25% of it's original strength, while the second only dilutes it to 90%.
Now, if you're looking to maintain a specific PG/VG ratio throughout this, that can make it terribly complicated. I can't recommend being very specific about that, unless you have a very good e-liquid calculator, or don't mind doing a lot of math.
That said, if you can get the nicotine liquid in the same ratio as your existing liquid, then you need not worry about it changing the ratio. Otherwise, a strong nicotine liquid will change it less than a weak one would, just as it also affects flavoring less.
