Cardinal tetra strange behaviour
Today I went and got 8 cardinal tetra's for our aquarium.
I see that 7 of them are healthy and normal but the 8th fish is behaving very strangely.
It does not swim with the other 7 fish, the way it swims is very strange it goes up to the surface often, stays hidden inside plants a lot of the time.
Im worried it might be sick.
I'm not yet very experienced at having an aquarium as this is our first tank.
It's a jewel 110 litres tank.
I've tested for nitrite and pH and both values are ok I think (nitrite 0.05mg/l and pH 7.0).
The tetras are together with 3 black mollys and 2 marble biota (I hope that's the correct name) and I don't see anybody harming the tetras.
I've uploaded a video of this specific fish here:
Does anybody recognise this behaviour?
Should I be worried or will this correct itself?
Many many thanks in advance for your assistance!