Bad Red Sea pH test kit?

[davidcalgary29]

I've been consistently testing between 8.0 and 8.2 with my Red Sea pH test in my 2g jarquariums. I also acquired a HM digital pH pen, which was way out of whack -- it consistently gave readings of 9.0-9.1, which I thought to be highly improbable, so I acquired some pH calibration solution off of Amazon (yes, yes, but I don't have a LFS). I recalibrated the pen with the 7.0 solution and then tested it with the 4.0 solution -- readings appeared to be spot on. Actual readings on the jarquariums, though, resulted in pen readings of 7.8-8.0. The Red Sea test, though, is showing between 8.2 and 8.4. (it was off the charts before I added aeration and removed some macro).The Red Sea test hasn't expired. SG is at 1.025 in both at 26C. Am I stuck in a guessing game? Do I simply bite the bullet and go for a conductivity test? Nothing really rides on this right now, but I like to keep my macro and lone mushroom frag happy...and I am starting up a Fluval Evo. Thoughts?

 

[Brandon3152134]

Not sure never used red sea. But wouldnt using rodi water be just as good of a neutral solution since it would have ph of 7

 

[davidcalgary29]

Well yes, and I do have a unit (and I even have some distilled water in the house, too), but I wanted the 4.0 solution as a failsafe as well as the Electrode Storage Solution (for both this and my DO unit), which is nearly impossible to get in Canada; the 7.0 solution was just a bonus for me.

 

[Randy Holmes-Farley Verified Community Expert]

Calibrating a pH pen with pH 7 and 4 is not optimal since the pH you are measuring is outside the range beign measured, but it is likely more accurate than the kit.

I'm not a fan of pH kits as there is no easy way for reefers to verify the accuracy (like a calibration or even a test measurement),a nd I'm also not certain if all hobby companies even understand that the color change of dyes may be different in seawater than fresh.

 

[Randy Holmes-Farley Verified Community Expert]

Not sure never used red sea. But wouldnt using rodi water be just as good of a neutral solution since it would have ph of 7

Definitely not.

Even if you got totally pure water out of the RO/DI, CO2 will enter from the air and lower the pH.

Also, since it is unbuffered, very tiny traces of stuff swing the pH wildly, and pH cannot ever be measured accurately with totally pure water using a normal pH electrode due to the very low ionic strength.

 

[Brandon3152134]

Definitely not.

Even if you got totally pure water out of the RO/DI, CO2 will enter from the air and lower the pH.

Also, since it is unbuffered, very tiny traces of stuff swing the pH wildly, and pH cannot ever be measured accurately with totally pure water using a normal pH electrode due to the very low ionic strength.

Good to know was just curious thank you.

 

[davidcalgary29]

Stupid pH pen! I was testing 7.5-7.6 throughout the day. And then fretted and plotted. And considered dosing kalk, which fried all the algae in my jarquarium. And then decided to retest with my calibration solutions, even though I just calibrated the pen. And watched the pen's readings drift down to 3.7 and 6.7 on my 4.0 and 7.0 solutions. The Red Sea test shows 8.0-8.1 and dKH is at 11. Bah! I need to stop reading low pH threads and leave the water alone. The macro seems happy enough, anyway.

 

[davidcalgary29]

Just tested with the Red Sea kit again. All three are from same jar at 1.025 SG, 12 dKH and 26C. Second test (blue, middle) was taken one minute after the first (amber, left); third test (blue, right) was taken twenty minutes after the second. Bottle was agitated for ten seconds on each occasion, as was the sample of water before drops were added.