Danios aren't going to the top of the tank?

[Llama_13]

Hi guys!

I recently started a tank (8.5 gallon warm FW).
Two days ago, I got my first few fish: 3 Golden Zebra Danios & 3 Longfin Leopard Danios.

I remember that when I researched Danios, I read that the mainly chill near the top of the water. Mine, however, are staying near the bottom of my tank. They only come to the top if I open the lid or feed them, but as soon as they finish eating it they all go back down to the bottom.

Is this due to stress, or is there a reason they're acting like this?

Thanks!

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(PS: one of the Golden Danios looks much younger and smaller than the others. He/She isn't schooling with the other Danios, but is rather hiding in the corner or near the shelter I got for my Khuli Loaches [<--- Haven't got them yet] Should I be concerned about it?)

(PPS: So far I've seen no aggression among them, but the biggest Danio (a Longfin Leopard) occasionally chases the others (particularly the Goldens). I'm presuming this is just an act of dominance?)

 

[Fresh2o]

When I had danios (longfin blue) they would hang out at mid to lower levels. This was in a 20g long (foot print of 30"x12"). These are active fish and really need some swimming space.
There was an alpha female that occupied about half of the tank and would chase any other fish that would invade her "territory".