Sudden Orp Drop

[Gieser]

Today, right after I did a 35 gallon water change, my Orp suddenly dropped to 150. It has stayed there ever since. My probe is a NS probe, and I have not calibrated it in a long time. I don't have a calibration fluid. It always ran between 250 and 280 on a regular basis. I have an ozone system, but have never set it up, yet. Not sure why it dropped so dramatically, but I'm worried, although the livestock seems fine.

[Randy Holmes-Farley]

What salt mix did you use for the water change?
Livestock generally do not care about ORP. I'm not sure most organisms even have a way to sense it. What they care about are particular things in the water, and ORP overall is not a good way to judge what things are good and what are bad (lower ORP does not mean inherently not less desirable water), but it can give clues about certain processes.
New salt mixes often have very low ORP. Probably due to the types of metals like iron that are present.
If the ORP comes back up, I wouldn't worry about it. If it stays low, you might look to cleaning the probe and recalibration/checking of the ORP reading. :)

[Gieser]

What salt mix did you use for the water change?
Livestock generally do not care about ORP. I'm not sure most organisms even have a way to sense it. What they care about are particular things in the water, and ORP overall is not a good way to judge what things are good and what are bad (lower ORP does not mean inherently not less desirable water), but it can give clues about certain processes.
New salt mixes often have very low ORP. Probably due to the types of metals like iron that are present.
If the ORP comes back up, I wouldn't worry about it. If it stays low, you might look to cleaning the probe and recalibration/checking of the ORP reading. :)

Thank you for the insight! I used to use Red Sea Pro and always liked it, but for the past 6 months or so I have been using Instant Ocean Reef Crystals. I will keep a eye on the probe and will re-calibrate it. I have been using it for a long time (3 years), so maybe it's wearing out.

[Randy Holmes-Farley]

Reef crystals has organic matter in it, and especially if that is allowed to degrade before using it, the ORP may be pretty low.

Try measuring the new RC, and maybe even over time as it is stored. :)

[kaipo13]

As someone who works in a lab....

Calibrate, calibrate, calibrate!

If you can't be sure your instrument is correctly calibrated than your reading is almost meaningless. Endless times people have set off chasing problems that were either wrong or non-existent, due to sloppy lab work and simple non-calibration of test equipment.