User blog comment:FairyRaven/Fairy Tail Chapter 396: Air, Review and Commentary/@comment-74.61.219.92-20140813063447/@comment-7418318-20140813202810

Virgo and Loke were blasted by Jackal, so most likely they can't come through even if they try.

As for Horologium... it was never very clearly defined how he comes through on his own, but judging from his explanation why he saved Wendy from Hades, but didn't come through when Lucy was in danger before, I'd say he can only sense high-powered attacks.

Poisonous water wouldn't carry much of an energy signature (or whatever you want to call it) and thus would likely not trigger is emergency mode. Or maybe the entire area is so overflowing with magic and curse power from the all the fighting and the CSKs rampage that he can't sense anything.