Hi

you ask for a trouble shooting guide.

This and many other helpful resources for the KHD, such as videos, knowledge base, etc., are available on the GHL support page:
https://www.aquariumcomputer.com/support/

Maintenance guide - not available since there is not much maintenance to do. Calibrate probe from time to time, replace filter when dirty.

I guess your dosing pump calibration is not correct or something is wrong with the tubing. All explained in above mentioned support resources.