Unfortunately I had to retire my old friend, my Blue Lab pH meter. Served me well over the years.
I replaced it with a Apera. Nice unit, fast, accurate. But I have a question.
The cap that covers the sensor has a fill line.
What am I supposed to fill it with?
Ph probes need to be stored in solution to remain accurate.
I can offer my experience and what little knowledge I have on the subject. From what I understand, and I definitely could be wrong, the storage solutions above are used for long term storage.
I have the PC60 model Apera. It doesn’t have the fill line but when I got it, it said it was sent with a little water in the cap to keep the bulb moist. For whatever reason, I started filling the cap with tap water to about where the line is on yours after every use for about 2 grows. When I broke it out for the 3rd grow, the EC probes were no longer working.
I spoke to Apera customer service and the rude Rep told me I needed to replace the tip and that I was only supposed to have been using “2 to 3 drops of water in the cap”. I asked if I should use the Apera KCI solution I had purchased and she replied “2 to 3 DROPS of water, sir” to which, after clearing my throat, I said OK.
Since, I have been doing just that, 2 or 3 fresh drops in the cap every time I use it. If there’s a stretch of time between uses, or grows, I use the storage solution. That is just my experience. You can’t go wrong with the KCI solution though. Oh, btw, the EC probes started working again that grow and the pen is still working and is still accurate after 4 or 5 years now.
HA! I said I had the PC60. It’s the PH60, and it comes with the same calibration fluids PH20 comes with but it also had containers with marked level lines on them to calibrate in that yours doesn’t seem to have. My best guess is that is the calibration fill line.
I have the same pen, the guide says to just use water but I use storage solution. I think you could use either and be fine.
I rinse it in water and put the cap on with it wet, but I accidentally leave it out sometimes all day without it ever being an issue, though it would probably last longer if I didn’t do that. I check it when I think its giving me a reading it shouldn’t. I know when I mix my nutes what the ph should be when Im done. If its off I calibrate it and check my nutes again before feeding. Be careful green algie will grow in the cap, it needs to be cleaned every now and then.
Yeah, mine has grown some pretty scary things on it when I don’t put it away properly. 
Im pretty rough on my meters but I also make sure they’re accurate because of it.
Left mine out of the cap for months. Just used it everyday and left it wet. Never really drifted much. I did clean it once a week with a little brush. Broke the bulb. 
Didnt have one for 6 months. Bought a new one… forget to use it.
