Waterkwaliteitstester, Waterkwaliteitdetectiepen Smart 7 in 1 Hooggevoelige Sonde PH TDS EC ORP SG Zoutgehalte Temperatuurmeter

Initially, when I opened this water tester I thought it was amazing and extremely good value. I have previously owned an ORP tester and a pH tester a good few years ago and they were much more expensive than this unit.You get a whole load of sachets for calibrating the pH, the unit comes with batteries and a good instruction leaflet. Even more impressively, it connects to an App on your phone via bluetooth. It tests 7 qualities of water and the instructions show how to calibrate it for each metric. Such amazing value I thought.I installed the App on my iPhone and it connected straight away. I like everything about this apart from when I started testing stuff.Now I should say that as I don't have any distilled water, I haven't calibrated the pH, or any of the other items as I don't know how to get a 256mV solution for the ORP calibration nor how to get 1413uS/cm standard solution for the salt levels. It would appear that you need to buy specialised buffer solutions elsewhere and these can be quite expensive. Its a shame they weren't included as it could well cost as much as the meter just to get the calibration solutions. I'm making an assumption that there must be an initial factory calibration done before shipping, but this isn't explicitly stated. I would assume though that even if the readings aren't 'absolutely' accurate, they will be consistent and relative?I've attached a summary of the readings I saved. The first one (at the bottom) was a glass of filtered water.The second reading was a glass of allegedly 'Hydrogen water'. The third and fourth readings were the same glass of tap water literally a minute apart. The two last readings was our pond, literally a minute apart.The first thing I noticed is that the temperature is all over the place. I checked it with a Thermapen and it was as sometimes over 15C out. I also used another thermometer to verify it. On cold water it was sometimes within a degree or two, but sometimes 5-10C out. I worry that if the temperature is wrong, what faith can I have in the other aspects that I can't verify?The two tap waters (reading three and four) are literally the same glass of water a minute apart, yet the readings differ significantly. I'm also surprised that the pond has significantly less dissolved solids than the drinking water and that the filtered water has more TDS than one of the readings of tap water.So in summary, I'm certainly no expert in these matters, but I can't make much sense of these readings and I don't really have much confidence in what the meter is telling me due to the variance in consecutive tests. Its a nice functional machine that doesn't cost the earth, but for me its a bit of a let down.