I agree this is likely a matter of lack of cover. If you could post the test numbers asked for by Naughts it would confirm (or not, as the case may be). But both neon tetras and Ember tetras are quiet fish. They will swim but never to the extent of the guppies or panda cories which are both more active fish. Floating plants would help a lot here, and the background suggested above. Plain black construction paper works very well, you don't want bright picture backgrounds to clash with your plants and fish; a piece of construction paper cut and taped on the outside back wall will work well, I have this on all my tanks.
And you should get a few more of both tetras; 8-9 of the neons and another three Embers would help too. I cannot tell from the photo what the filter flow might be like, but there are ways to reduce the current down the tank if that is needed.