New Fish...

[SyncereOne]

I picked up 8 blue turquoise discus from a guy on craigslist about a week ago. I am new to discus, but not to FW fishkeeping, and at $5 dollars a piece, I couldn't lose. I wanted to make sure I can get the hang of raising them before I buy some of more expensive fish. Right now they are about 1-2" in size. Most of them are showing good coloration so far, except 2.

They go through phases where they turns dark, then the next day they looks fine. The fins aren't clamped, and I don't see any other signs of disease. The other fish are okay, and swim all over the tank, but these 2 stick to the corner when they are dark. I assume they are stressed, but I don't know whats doing it. My tank temp was around 86-87 degrees, but I've bumped it down to 84.5.

Tank params are as follows:

37G barebottom, cycled tank. (until I get 55g ready)
1 AC70 with 3 foam sponges, 1 AC50 with Efisubstrat Pro
Airstones
40% daily water changes, aged, heated water, treated with Prime.
Nitrite 0, nH3 0, Nitrate 5ppm, pH 6.4. (tap 7.0, aged 6.4)

I'm feeding them beefheart and flake, and all the fish are eating, even the dark ones. The only thing I can think that may be bothering them is that this tank does have a dark background.

[Apistomaster]

The new fish sound like they are still adjusting to their new home.
If you place even a black plastic garbage bag to the back as a temporary background and provide them with some potted plants and bog wood, they should soon settle in. Discus also like cover including some floating plants like Water Sprite or Hornwort. Sprinkling a thin layer of sand is also good. Doesn't make it harder to keep clean and discus like to forage through the sand for food. Just enough to conceal the bare bottom glass can make a difference; use 1/8 to 1/4-inch of sand.
Young Discus are naturally shy. They become bolder with each month of age.