Montipora help. Possible hydroid damage?

[Morrowen]

Yesterday I noticed a patch on one of my montiporas that was discolored and had no polyps showing. Later that night I found a Digitate Hydroid brushing up on the same spot that is looking damaged. Are hydroid actually capable of doing this?

 

[vetteguy53081]

Yesterday I noticed a patch on one of my montiporas that was discolored and had no polyps showing. Later that night I found a Digitate Hydroid brushing up on the same spot that is looking damaged. Are hydroid actually capable of doing this?

Hydroids are known to sting. I see a strand in the back that may be one of a vermetid snail
Assure good flow which will prevent them from getting food

 

[Morrowen]

The white string in the center of the image is the Hydroid I am concerned about. Not sure if that is the strand you saw. Depth doesn't come through well but it is in front of the monti.