Thank you
@jaypeecee for your comments, they are interesting.
My responses are more for anyone else looking at a Seneye - they're not cheap, so it is good to have as much information as possible.
1. My pH does read higher than I expected, but I only using liquid tests as an alternative, so always assumed the Seneye was the more accurate. To be honest, I'd be happier if my pH was a little lower, so it's fine for me. And I do have low hardness.
2. I appreciate that the Oxygen reading given is calculated based on temperature, so I don't really use this. As far as I am concerned, the Seneye makes no difference to me on this because I didn't measure my oxygen levels prior to using the Seneye.
3. I've had a few discussions about this. It is different to the results from a liquid test, but I've not got it straight in my head what the difference actually means. For my use, I don't get too worried about the actual number (each slide seems to be to be slightly different calibration), but keep an eye on the trend, as long as it stays in the green "safe" part if the chart.
I've been using my Seneye for 3-4 years, on and off now. I noticed at the last slide change that there appeared to be water inside one of the sensors (only enough for me to keep an eye on, not worry yet).
The thing that I've found most frustrating is that my Seneye often loses data instead of uploading it, when it's been monitoring offline. I'm reluctant to spend more money on it (buying the server and Wifi units), but it bugs me that I have to leave the laptop running for it to work properly.
I went away for a week over Christmas and deliberately didn't look at the data online. There would have been nothing I could do if something went wrong, and it would have ruined my holiday if I new my fish were dying!