help!!!

i just added some neon tetras to a well established tank. pH:7.2 Ammonia: 0-0.25ppm Nitrite: 0ppm Nitrate: 0-5ppm they’re just sitting in one spot kinda twitch swimming?? not sure how to describe it. will post a video in the comments. i’m concerned maybe they’re extremely stressed out? they came from a pet store sell out in my home town and were in a tank with a bunch of other dead fish.
Currently in a 20g standard w snails