Looks nice Shih!
You can control the flow rate and duration of dosing from you Apex with that doser, and save the LCD / control interface part, if your friend can find you the DC voltage control interface, oftentimes available on the driver boards, in addition to the usual RS-232 interface.
My DIY doser uses very similar stepper motors like yours, and the driver board takes a 0-3.3v DC control signal to vary motor speed from 0 to max. With 3 identical resistors of 10k each, you can connect to the variable 0-10v DC output on Apex (V1/V2 or V3/V4). Create a profile and tune the voltage to calibrate your dosing speed, and use a OSC statement to control dosing schedule say 30 seconds per hour, use IF TIME statement if you want to specify which hours you want a particular dosing head to run or not run, and you can use one or more of the 4 feed timers to do things like, say adding 10mL extra alk, etc, with a single click of the feed button across the internet, assuming you have feed buttons available with no associated actions yet. The only thing missing is something like your alk monitor, with input from it, and a doser controlled by Apex, alk level can be automated, with precautions of course, for example, pre-set up-limit and alarm thresholds etc to prevent disaster from equipment error.
