:-( You are totally right and that sucks for me. I will be purchasing a higher nicotine strength tonight!! Thank you!
If you have a 30/70 0mg base, then adding nicotine will change those numbers.... unless you have the same 30/70 nicotine base.
Most people use a very high nicotine base, and dilute it down to the nicotine level they want. I use a 60mg/ml base of pure PG, and get my flavorings in PG. I am more worried about the nicotine content and the flavoring percentage than I am the PG/VG mix. I like a fairly high VG mix, so for me, I don't even factor in what PG/vg mix it is... I just calculate it for 6mg with %10-%15 flavor (depending on the flavor) and fill the rest with VG. I would guestimate my VG is in the %80-%90 range which is good enough for me.
There would be two methods to use... the Simple method, and the DIY method.
The simple method is simply buying the nicotine base at a slightly higher mg/ml level that you want. if you want, say %10 flavoring, then you would ask for a 3.3mg/ml base.. when you add the %10 flavoring, it would dilute it back down to 3mg/ml. The good point on this method, is it's super easy.. just add flavorings. The downside, is numbers will be always approximate, and chances are, finding an exact nic base, I wouldn't hold them to a .3% margin for error..
For DIY: If I were to try and make a %30pg, %70VG, using PG based flavors, and PG based nicotine at a 60mg/ml.. for 30ml bottles, I punch up
steamengine.org and go to the eliquid section on the top. put in 30ml for the batch size (the size of the end bottle) change to mg/ml, then punch in 60 for the mg/ml under the Nicotine base liquid.
Then for flavoring, I would put it.. say, for %15 flavoring for flavoring one... and make sure it's PG flavoring. Then I go over to the Target and put 3mg/ml as the desired target and the 70VG/30VG target level. The mixing part should now be filled in with what I need to add, and what levels. It tells me how much of what to add. For this, you have more control over your liquid mixing, but you'll be the margin of error... it's only as exact as you are. Also, mixing with a high Nic base, you should be careful and always use gloves and do it in a well ventilated area.
Just remember, Mixing and DIY juices can be fun... don't get too caught up in the numbers except for the nicotine. Also, if you were to resell it, I'd be concerned about making recipes that are duplicatable (if there's such a word). as I said earlier.. for me, it's not exact, it's more fun than a chemistry experiment. Nicotine levels is the only thing I am super critical of.. the rest.. well, it's just fun. I seem to have a few followers when I let them try my juices.. they seem to like it. My favorite overall, is a Guava and Vanilla custard blend