grammar, link to customizing probes section

Author: josh-heyer

product_docs/docs/pem/9/monitoring_performance/probes.mdx

@@ -12,7 +12,8 @@ redirects:
 A *probe* is a scheduled task that retrieves information about the database objects that are being monitored by the PEM agent. PEM uses the collected information to build the graphs displayed on each homepage. The **Management > Manage Probes** tab allows you to modify the data collection schedule and the length of time that PEM retains information returned by a specific probe.
 
 ## System probes
-System probes are monitoring probes predefined by PEM, which definition cannnot be modified. Use Custom probes instead, if any changes are preferred.
+System probes are monitoring probes predefined by PEM. You cannot modify the definitions of these probes. If you need different behavior from a probe, [define a Custom probe](#customizing-probes).
+
 Unless otherwise noted, Postgres Enterprise Manager enables the following probes at the server, database, schema, extension (starting with version 8.4), or agent levels:
 
 | Name                                     | Information monitored by probe                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       | Level    |