weird gourami behavior

[Fish Novice 12]

I have 2 blue three spot gouramis and I have had them for around 3 months together.( ive had one for about 4 months longer than the other) lately I bought a new pleco for the tank and everything seemed to be fine at first, but now it has been about a week and things are going downhill. The older gourami started picking on the little one, causing fin damage. Also the older one has been acting weird like sitting at the bottom of the tank and hovering back and forth a lot. I now have them separated. Is this normal when you add a new fish to the tank or is it some kind of disease??? Please help!

 

[Joshfishguy]

Is the fish eating

 

[Fish Novice 12]

Yes hes eating just fine

 

[Wiggles24]

Blue gouramis WILL NOT tolerate each other. Even if they do OK for a little while it will end bad.

 

[Fish Novice 12]

Does that explain the weird behavior?