Not exactly an answer to any of the questions (sorry, I always, plant, watch, play by ear, repeat lol), the morning glories will most certainly not flower if there is too much nitrogen in the soil. I've never tried to un-nitrogen it, but made the mistake of adding a nitrogen fert (twice!) before I realized it was stopping all flowering for a long time.
I have heard of people mixing a small amount of apple cider vinegar in when watering, to help keep gnats away and reduce salt build up in potted plants, so it should at least not be too harmful if you wanted to try that route.
The morning glories probably want more sun, if that is possible. They seem to flower best with a decent bit, and since you're in Zone 5, it is likely not as hot or sunny as where I am.
Also, they may not overwinter. Mine set seed every year and replant themselves (morning glories will seed profusely if they get to flowering), but I don't bother trying to move them indoors overwinter. I save that space for more rare plants. Once you find a spot they like, and get them started early in the Spring, you can have plants that go from seed, to huge vine, to flowering and seeding, within a growing season.
I have seeds for Heavenly Blue, Grandpa Ott's, and I think Flying Saucers, so if you ever need more seed to give it another try, just let me know.