quarantine stress

I've finally joined the quarantine bandwagon, and put my newest acquisitions in quarantine. My concern is that the fish look really stressed after being the quarantine tank for almost 20 hours. My previous acquisitions all colored up again within an hour or two after being released into the general population of my display tank. Is this normal? They're eating okay, but they're staying real close to the bottom of the tank. The new acquisitions are 6 glow light tetras and a rummynose tetra, that will be joining the rest of the ones I already have; I just couldn't leave a lone rummynose at my LFS.

The water parameters tested the same this morning, 0 ammonia/nitrite, 10-20 nitrate, and pH 8.2, 76 degrees as the display tank.

No cover in the tank. It's bare. I don't like it looking like that, but the prevailing thought is that it makes it easier to dose/clean if necessary, so I followed the suggestion of the masses. Think it'd be okay to place a piece of artificial decor in there? I have two in my display tank, basically to provide molted shrimp fish free zones (pretty small openings) to hang out in.

It's a 10 gallon tank, so by any measure, it should be understocked, and I just pulled a filter off of my display tank and let it run full bore for almost two hours (it's a Top Fin 60, so should've really moved most if not all of the water at least once during that time) before cutting it back to about 1/3 flow, and releasing the fish in there. And yes (since I know it's a logical question that'll likely be asked), I did a slow acclimitization, about a half hour for temperature match, and then added some of the tank water to the water in the bag every 30 minutes for the next 90 minutes, and a half hour after the last addition, removed the fish from the bags, released them into the tank, and discarded the LFS water. Some may have gotten into the tank, but I doubt it.

My biggest concern is that my previous fish have all colored up nicely within 2 hours of being released from their bags. We're looking at about 22 hours now, and they're all very pale still.