I gave up trying to cycle the QT. I did everything I could think of to give it an 'instant cycle'- I swapped sponges off the little filters, sterilizing the QT one (which had only been in there half a day) and moving over the one from the main tank, which should have plenty of bacteria in it. I siphoned a handful of gravel out of the main tank, tied it into a piece of pantyhose and put that in the QT near the filter. Dropped in a few snails and a food wafer (the snails congregated on it, so they're feeling fine). Checked on the water quality a few times each day. Did another water change to see how that alters parameters. Ammonia is still worrisome- it's 0.5, when I do a water change that brings it down to 0.25 but it goes back up again.