Yeh, expecting a breakthrough in a single hit EVERY time seems like high standards, especially with a bong. As far as I know (this is a debated topic), there is no tolerance increase which you should be worried about. As gammagore said, just smoke on until you get to the right place...
If it's still too weak then sure, you could add a little more spice. And if it's too strong then, add a little herb, etc, etc etc...
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