20 minutes or so is fine. It's totally fine to use in RO water just don't store it in it. As long as you always keep it moist and store it in 7.0 solution in between uses and KCL storage solution if it's not being used daily. If it is being used daily then maybe monthly leave it in KCL overnight to recondition it. It will stay in tip top shape for a long time.
Hey, just thought I would add something to this conversation. I had contacted blue labs prior to asking y'all about how long probes could be in ro water but hadn't had a response from them. I just received a response in asking about how long the probes could be in RO water to test its pH. I asked if 20 minutes was too much exposure.
Here's their response;
"To clarify, unfortunately you cannot test the pH of RO water, as it does not have any ions for a pH probe to take a pH reading from. This is how our pH probes work - by actually taking a pH reading using the ions that are inside of the solution being measured.
Our pH probes (and most pH probes in general) are charged with a lot of these ions when they are made. This gives them high ionic content. What happens when you place them into a solution of little or no ionic content (such as RO water) is that the solution then tries to pull the ions away from the pH probe that has been inserted (nature tends to try to balance). This then actually damages the pH probe and also may cause a false reading on your meter.
To get around this, simply add something to your water to bring the ionic content of the solution up (which can be measured in EC or PPM). Most growers find that any solution higher than about 0.3EC or 150PPM (500 scale) / 210PPM (700 scale) will give a more stable pH reading.
Please feel free to come back to us if we can help further with anything else.
Thanks again for contacting us!
Best Regards,
Tua | The Bluelab Team"
Sooo pretty much what you had said except that they didn't recommend testing the pH of pure water/RO water whatsoever.
