Obviously it would be best to ensure that you know the concentration of the juice by having prepared it yourself.
Hopefully, somebody with more experience regarding vape pen tanks will chime in soon because there's nothing I can add on that matter.
It would in principle be perfectly feasible to increase the concentration of DMT in the juice by adding more yourself, although this kind of circles back to the first point since you've ended up essentially having to prepare your own juice at this point.
Ditto as regards the identity of the substance used, although it's far more likely to be DMT and basically extremely unlikely to be 5-MeO-DMT in there. If you want to know the identity of the compound(s) in your juice, you'll have to send it for analysis at somewhere like Dancesafe, Energy Control, or maybe our very own Solaris Analytical. Reagent testing kits will give a fair indication if used in the right combination, as will careful use of a TLC test kit.
One more thing - please ensure that you take the time to have a read of the attitude page (link below - and, indeed, above) and adjust your posting accordingly.
“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli