I'm 1 week into this tray. There is a gap at the bottom. Should this disappear when it’s time to change my trays? (photo)

Hi there!  Nice picture.  It seems that the tray is slightly not tracking properly.  What I like to recommend for my patients to do is to bite on a suction tip (or anything else that you can find that is hard enough) that will help slightly shift the teeth into the position of the trays.  Assuming you are otherwise tracking properly in each aligner, your teeth should settle right into those places and the small gap should go away!  Great job in keeping your teeth clean! 

Teeth don't always move the way we want them to and its difficult to say whether the gap will close or not. If the gap continues or worsens I would check with your treating dentist. If you aren't wearing your trays as often as you should, they're not going work the way they are supposed to. I would add an additional day if you ever feel like you left them out too long to ensure movement, but even then there can still be lack of movement. 

Hi, thank you for posting a nice photo. Yes , your gap will disappear by the time you are ready to change to next set as this is the gap where the aligner is moving the tooth. Here , since the teeth are being pulled down to close the bite, you will have similar situation in most aligners till its achieved. Hope it helps.