I know there are many issues of fish not swimming, but I can't find anything related to my situation.

I bought 3 celestial danios a few weeks ago. One died, so now I just have the two (1 female, 1 male).

In additional to them, I have a coolie loach, 6 shrimp (red fire/yellow), 2 fan shrimp, an albino algae eater, and 3 other fish (similar to neons/cadinals) I also have plenty of real plants in the tank.

The tank is a microtank (about 8 gallons) and was really well balanced, and the water rarely needed to be changed.

Okay, now all that info is out of the way, 1 of the danios has recently started to stay in only one spot of the tank. She sits at the top right corner of the tank and stares out of the tank at a wall. She swims fine when chased, she eats, she's up right, but still stays in the one spot. This has been going on ever since the other danio died. Also, since the 1 danio died, the male chases the female around whenever he gets near her.

Any ideas of what is going on? It took me over a year to find these fish and I'm concerned about losing them.