Can you please take a screen shot of your weekly KH graph combined with your soda ash graph. I do not know anything about how to program for automatically control KH but if the fluctuation is periodical - it is caused of your type of dosing. As I understand - your settings now allow the KH to drop to around 8 before the function starts. It is possible to set the deviations in decimals. Is this only an extra feature or are your pump scheduled too?
I have not test this method but if I would - I´l start to figure out how much alkalinity my tank consume. I would do this by shout down all dosing during 24 hours. Use 4 (or more) analysis a day and have the "always test time" to the time the light shout down in the evening. When I know this - I can start to figure out how to program. If you have a 24 period with no dosing and rather much testing - you will see when the tank consume max.
When I break up my dosing to be different between light and dark period - I run the test every hour for 24 hours and stop all dosing. I got a very good picture when my tank use alkalinity or not. It ends up to a dosing of 14,4 ml (36 dosing of 0.4 ml) during the period 00:00 to 11:59 and 38,4 ml (48 dosing of 0.8 ml) during the period 12:00 to 23:59. Did I get a more stable KH - both yes and no. Because that my system vary in its demand of alkalinity - I get changes in the KH but rather slowly. Below is my KH for last month - Red arrow - rise of dose of Core7 3a+b during daytime. I use Triton Core 7 system. I test 2 times a day 06:00 and 18:00 Blue staples is my actual dosing.
Normal photoperiod is from 8 to 23. Max illumination between 15:00 and 18:30
Honestly - I´m not so interested of the actual value - more of trends
When I talk about how I manage my own tank - I´m normally send with a picture or video of the tank - here is the last video showing most of the tank
Hope that this give you some ideas how to use the KH director.
Sincerely Lasse
