Aquariums: Neon tetras died and now I face a dilemma

I’ve had this tank for almost 2 months and just finished stocking it. I started with one batch of 4 neon tetras; after a few days one of them passed away. When my LFS finally restocked a week ago, I bought 3 more for a total of 6; one died a few days after and I’ve just come home today to a third death, leaving me with only 4.

For one, I’m confused at to why I keep losing them. I included a picture of my water parameters; the tank is decently well planted (as much as I can afford to at least), the pH is at 7.4, and the water temp is 78°. I’m new to this but I can’t immediately see anything wrong with the water that could be causing it.

Secondly, now I have a dilemma with restocking the tank. The smallest tetra immediately becomes aggressive anytime the school is too small and almost constantly bullies the others to the point where they stop schooling. Normally I would immediately buy more tetras to fix the problem, but I’m taking a flight tomorrow afternoon to visit family for Thanksgiving and will be gone for a week. I don’t know if it’s better to risk leaving them alone with the bully fish or better to risk buying new ones and hope they survive the week while I’m gone. What do you guys think I should do???