Found it:  ./includes/alerting/slack.inc.php

Thank you

From: observium <observium-bounces@observium.org> On Behalf Of Mark Carter
Sent: Tuesday, May 29, 2018 10:42 AM
To: Observium Network Observation System <observium@observium.org>
Subject: [Observium] file that controls alarm output

Hi, what file controls alarm output?  I have alarms going into a "Slack" channel and want to format them so they take up less lines.
Currently an Alarm takes up 7 lines.

Thank you
Arthur