Engineer Gobies Fighting

[Plesoine]

I have 2 Engineer Gobies in a 180 gallon Tank. I've had them for over 10 years and they were always hanging out together. All of a sudden the one is beating up the other one and won't let it back into the tunnels. Does anyone have thoughts on why ?

 

[Gumbies R Us]

Did you make any changes to your tank recently?

 

[Plesoine]

Everything has been the same except I added a Algae Blenny about 6 weeks ago.