Hammer head is closing up

[Qasim]

Hi my hammer used to do very well. It even split into two heads but now one of them started to close up and the mouth is a little bit opened up. Any helps and suggestions would be really appreciated. If you notice from the photo the head in the back is doing well but the one infront closed up.

 

[vetteguy53081]

Hi my hammer used to do very well. It even split into two heads but now one of them started to close up and the mouth is a little bit opened up. Any helps and suggestions would be really appreciated. If you notice from the photo the head in the back is doing well but the one infront closed up.

It is stressed and likely causes are:
Too much flow
Insufficient lighting
High phosphate/nitrate
Lack of feeding
Low calcium (at least 380)
Pests

They do best at lower third of tank but not on sand