You might be able to do this with a restful sensor and avoid all that nasty regex as rest sensors convert xml to json. It will use less CPU resources. Regex are quite intensive searches.
rest:
- resource: http://IP_ADDRESS_OF_PM/cgi-bin/webgui.fcgi?xmlitem=34.4033
scan_interval: 60
sensor:
- name: "PoolTemp"
value_template: '{{ value_json.pm5.item["@value"] }}'
unit_of_measurement: "°C"
EDIT: corrected value template. Roger confirmed it works on Discord.