Sorry about the rainbow fish bless him.
R.I.P.
Don't forget to rinse the bogwood well before you let it dry out.
Fingers crossed for the other rainbow fish.
Did you meantion anything to the lfs.
Might of climatised them to fast.
I thought it was flapping due to your slight nitrite reading.
If there doing the same at the lfs it can mean
Lack of 02 in the tank.
Bad water quality.
Overdose of meds.
Toxins in the water.
Parasites like gill flukes and other external parasites.
Ph shock.
Constant swimming at surface (dinoflagellates [free-living or parasitic], toxins, pH shock)
Gasping, irregular opercular beat, rapid opercular beat (bacteria, dinoflagellates, parasites, toxins)
Are the fish mouth open.
Ok bless them.
If they are not flicking and rubbing it leaves ph shock to bacterial infection.
I doubt it toxins in the tank.
You could add a med but it can finish them off if there breathing already bad.
I would increase aeration in the tank if you add the med.
Is your nitrite reading 0 yet.
Did you meantion anything to the lfs.
Might of climatised them to fast.