Checking the Ph of tap water

[Muz]

I'm new to Ph meters...

I'm trying to work out why my mash Ph has been coming in low.

I've calibrated my meter using three point calibration but I can't measure the Ph of my tap water. When I try it just slowly climbs from about 4.8 to the low 6s over 30 mins then stops.

I've read that measuring the Ph of soft and pure water is really difficult. I'm guessing that's what it is. Is there a way around this? Something I can add to the water that doesn't impact that Ph but makes it more conductive to readings?

Or does anyone else have experience troubleshooting really low mash Ph? I use BeerSmith to work out how much Phosphoric acid usually.

 

[MHB]

Your tap water is probably gassing off, they aerate water as part of the treatment process to make it taste better.
If you used distilled/de-ionised/ultrapure water. Over time it will equilibrate usually slightly acidic from Carbonic Acid created from dissolved CO2. Given that I don't know anything about your local tap water I have no idea where it will settle, mine usually comes in around 7.4pH give or take from just a touch of Carbonate.

If your pH is coming in too low, use less acid (I prefer Lactic Acid)
The other really important factor is to keep your pH probe wet, letting them dry out seriously shortens the life of the electrode, they will also take longer and longer to settle if they are dry or partly dry.

What is your mash pH without acid, that's really a much more important reading.
Mark