I've kept test results and notes in pencil on 5x7 cards for the last 5 years or so.
For the five years before that I logged all the same data into a custom web tracker.
When I switched (from digital to pencil), I imported the existing data into a spreadsheet to do a little manipulation and make some graphs.
https://www.reef2reef.com/threads/dosing-testing-results-chart-stony-coral-system.93864/
I can't tell you what to pick for your own needs, but
I might be able to help you decide how to pick.
Pick the tool you're
more likely to use, whether it's on a computer, phone or
pencil and paper. More tech |= better.
Try
not to pick a tool that's hard to get your data out of.
It's nice if what you pick makes it easy to import data into it.
Pencil and 5x7 cards excel in most areas of concern.

They are extremely flexible and adaptable. They can do graphing. 5x7 cards can even be pretty durable. They ride in my test kit box with me, so I'm never without my data, even in the deepest jungle.
Some digital tools are nice too.
For example, I used Tikiwiki Groupware for the web-based data collection and basic presentation. The online Tiki Spreadsheet function is (or at least was) pretty limited, so I used Apple Numbers for spreadsheet and graphing needs. (see thread link above)
The important part is that you do the logging
regularly.
The data has all the value. ;Happy
No data, no value. ;Happy