Congrats on quitting!
Depression after quitting is common for the very reason you pointed out, a drop in the WTA. However, if given time, this can and often does pass. You will start to experience improved mood, improved health, and with improved mood and health you do more and feel better. I see you started here just in December, thus probably quit around that time.
While WTA could help, remember that it needs to be part of a wholistic strategy. Eat healthier, drink more water, exercise, and see a counselor/PCP if it becomes severe or lasts longer than a few weeks. If you take care of your body and mind you will likely find that WTA are not needed.
However, this does not answer the question you had asked, but was merely an answer coming from a concerned counselor.
WTA can come in either a concentrate which will be added to your normal
e-liquid or as a premixed
e-liquid. Some people go through the day with using just WTA mixed liquid whereas other people will use it just in the morning or evening as needed. Simply put, once it is mixed, you use it like any other
e-liquid, but usually are satisfied enough to use it less often without intending to use it less often.