And don't judge a juice with just a few vapes. In fact, I sense the flavor develops after a half tank. Like maybe the wick and coils get broken into the new juice?
But I'd give each at least 2 tankfuls.
(This is where more tanks pays off. Yes, a bit pricey at $7, but they last a long time. I have 7, and all are hitting great after 7 months of hard use!!! I have no reason to think they won't be just fine after a year. I think an excellent return on investment.)