I just bought an Apera pH/TDS meter so I could get some reliable readings and after calibration with 4.0 and 7.0 solutions I am getting a really acidic reading from my RO water.
Is a pH of 3.24 normal for reverse osmosis water?
I have been reading that slightly acidic is normal around 5 but what’s up with 3.24?
I just double checked with my cheap pH meter and it gives basically the same reading. 3.21
I’m not sure about apera but Bluelab has issues with measuring pure ro. It seems most probes will have issues with ro and it’s not good to rinse the probes in ro because it can mess with the chemistry of the probe.
Ok good to know. Thank you for the information. I will make sure I don’t rinse in RO like I was doing. 
What should I be rinsing with? Distilled water or just tap water?
Hi @scryptic
A couple things I learnt about testers is check to see if it has a thin line of plastic covering the testing unit. I made this mistake once.
Calibration solution that can be found at most growshops is also a good thing to have handy to get more accurate readings. Rain water for me was the best to rinse in.
https://growershouse.com/bluelab-calibration-solution-27-7cf-ec2-77-250ml
With ro water u won’t or shouldn’t get a good reading h less there is a mineral adding filter inline also. There is nothing in ro water to leach to to get a steady pH reading. U can add ro water without phing it to any plant and it should take on the pH of the soil or coco added to. I tried with mine and it just drops real low pH and just fluctuates numbers never stopped on a set number by the time the meter shut off on its own. Did u get the calibrate solution with the pen believe it’s 4.0 and 7.0 run it thru a calibrate session it’s pretty simple to do.
I rinse with tap
@Mark0427 yes I calibrated with 4.0 and 7.0 calibration solutions. I had to order the 10.01 solution because it wasn’t included with the others which I thought was weird.
2 point calibration is good enough is why prolly. Lol. I’ve had my apera 2 years now only had to calibrate it 2 times and that was just to check after a grow to be safe. Never had an issue yet.
I always do 7 and 4, I think the 10 is if your measuring stuff above 7 but it might be different between apera and bluelab
