PostgreSQL + PG_Monz (Zabbix) DB size too large > 1073741824
I found the answer with regards to how and why this is happening. 
PG_Monz is using the following query to track temp bytes:

UserParameter=psql.db_temp_bytes[*],psql -h $1 -p $2 -U $3 -d $4 -t -c "select temp_bytes from pg_stat_database where datname = '$5'"


However, this select statement does not show the current temp bytes, instead it shows an increment of all temp bytes ever created since the last stats reset. IE: It's not showing a delta over a time period which would be the accurate number. 

Looking at this query and then checking the folder, I see it's empty and therefore my server actually has no temp bytes.

select current_setting('data_directory') || '/base/pgsql_tmp'


Source: https://www.marshut.net/wnsmt/postgresql-9-2-4-temp-files-never-released.html

The same goes for a DB being too large:

Zabbix threshhold is incorrect for the way PostgreSQL reports size of databases: 
See info about select pg_database_size(dbname)