Part of the consistency in parameters comes from age of the tank as well as your persistence in the maintenance program, this includes testing testing testing.
As you mentioned earlier you don't have alk or calcium tests. You absolutely need to monitor the parameters mentioned by
@vetteguy53081 and myself earlier in this thread for consistency.
Also, parameters never stay the same. Think of testing like a quick snapshot in time. Parameters like pH and alkalinity swing naturally throughout the day, temperature can swing based on the controls for your heater, etc. So it's good to pick a specific time and specific day(s) for testing and, at minimum, test at those times