Hi all,
They are a bit rough-and-ready and rely on your judgement in comparing the colour against the chart.
They work, but they are a bit rough and ready, and as you get towards pure water they become less and less useful. You can <"
specific range pH papers">, but they are quite expensive.
I just want to make occasional checks of the rainwater I’m using at the moment.
They won't help with this. If you don't have any carbonate buffering at all
<"they will read about pH6">, but as soon as get even a trace of dKH <"
they will read pH8.">
Although it won't tell you what the pH is, I still think you are better off with a low range conductivity meter, rather than a pH meter.
The advantage of conductivity meters is that:
- They are much more robust, and straight forward, to use then pH meters.
- You can make up your own calibration solution.
- They don't need regular re-calibration.
- The electrodes don't need regular replacement.
Even a £20 meter should give you a reasonably accurate result. Although it doesn't tell you what the pH is, it doesn't matter. If you have a conductivity value of 100 microS (64ppm TDS) then you don't have many ions of any description and you can add weak acids to reduce pH or weak bases to increase pH.
If you live on the coast you may get some Na+ and Cl- ions, if you live in land you can assume that most of the conductivity comes from Ca++ and CO3- ions picked up from dust etc. Our rain-water (Wiltshire) varies from about 150 microS (after they've cut the corn) to about 30microS in the winter. It is all limestone around us.
cheers Darrel