Neon Tetras won't eat

I had posted about 5 months ago about my first fish: several goldfish
and a betta. Although you might remember that all of my goldfish died,
my betta is still living well and strong! He's in a 10G tank, all by
himself, with a few artificial plants.

I recently decided to give him some company with a handful of neon
tetras (3, to be exact). Luckily, I had another 5G tank that I could
use for quarantine, which I filled about 1/2 way with water from the
betta tank (roughly 2 days after a 10% water change). The water temp
is 74-76, the pH was about 7.2, and there are no plants in the 5G
tank. I have a meter-thing that's supposed to change colors if
ammonia, nitrate, or nitrite reach dangerous levels, but since it's
never changed, I don't know if that means all is well, or that it's
not working; however, the betta has been OK, so I'm guessing it's
working.

From the get-go, the neons didn't do so well. I took a long, long time
acclimating them to the water (I'd say, roughly 2 hours of adding a
1/2 cup of aquarium water to the bag they came in, then taking 1/2 cup
out), so I doubt they went into shock, but the next day, one of the
tetras was already dead. A few hours later, a second one was dead. So
far, after 3 days, the third one is alive, but doesn't move around a
lot, and hasn't eaten yet.

Since he's alive, and will move pretty fast if I try to net him, I'm
hoping that maybe he's just in need of a good meal. I've been trying
to feed him TetraMin tropical granules, since that's what Wal-Mart (my
only LFS, and where I bought the neons) said they fed them, but the
granules are massive in relation to the fish's mouth so I've been
crumbling them up. Unless he eats after I walk away, the food moving
right by his face doesn't interest him in the slightest.

Any suggestions?