I have been in and out of saltwater for 25 years and have never ran a doser or Apex. I really like how the apex monitors and doses, but there are so many generations of Apex I have no clue what I'm looking for or what to get. I don't want to spend $1500 to set up a controller for dosing, so I will be buying used. I would like to use the app. What do I look for used to get a controller with dosing? I won't be using the controller for anything but monitoring parameters and dosing. I have my system set up the way I like it so far. I just would like to be able to monitor Ca, Alk, Ph, and whatever else I can monitor without having to test all the time. Thank in advance.