ORP Meter for Dissolved Oxygen

[bioload]

Can I use an ORP measurement as an indication of Dissolved Oxygen? Don't need an actual value for DO (or maybe I do) but looking for way to determine if anaerobic conditions exist based on ORP.

Any help would be appreciated.

 

[psteeleb]

Can I use an ORP measurement as an indication of Dissolved Oxygen? Don't need an actual value for DO (or maybe I do) but looking for way to determine if anaerobic conditions exist based on ORP.

Any help would be appreciated.

I don't think so

ORP is a measurement of oxidation reduction potential or a ballance between oxidizers (reducers) and larger molecules that you usually get from something dying or decayed food etc

for example an increase in chlorine or ozone as well as oxygen can give you higher ORP readings, or not feeding for a couple days could give you higher ORP readings

or as something dies in your tank you will get lower ORP readings

all of these reading changes can happen without a drop or change in oxygen levels

 

[Boomer]

Nope, they have no relationship what so ever However, the ORP meter can surly indicate if you have aerobic or anaerobic conditions.

Here is an example;

Hourly and Daily Variation of Sediment Redox Potential
http://www.nwrc.usgs.gov/wdb/pub/others/99-0001.pdf

The effect of several cycles of varying length of alternate aerobic and anaerobic conditions on redox potential
http://wetlands.ifas.ufl.edu/public...Effect of Alternate Aerobic and Anaerobic.pdf

 

[bioload]

Thanks for the help!

I must admit still trying to connect the dots on a lot of the information......not "light" reading. However....

Looking at the data collected from the study to determine the effect of alternate aerobic and anaerobic conditions on redox potential. It would appear that a prolonged anaerobic condition would coincide with a low redox potential somewhere in the range of 0 to -200mV? If so I can monitor and watch for a decrease in redox with all other things being equal as an indication of anaerobic conditions.

Or did I not get it at all?

 

[Boomer]

No, you seem to have gotten it all but measuring sediment with a std ORP probe is not the best or a easy thing. They use needle tip ORP probes.

 

[Boomer]

Here is some more stuff

Redox Measurements in Marine Sediments
http://www.geochemie.uni-bremen.de/downloads/redox/chapter19.pdf

PROBLEMS AND METHODS OF CONTINUOUS IN-SITU MEASUREMENTS
OF REDOX POTENTIALS IN MARINE SEDIMENT
http://www.aslo.org/lo/toc/vol_17/issue_4/0622.pdf

Sediments and Biogeochemistry
http://www.soest.hawaii.edu/oceanography/courses/OCN621/Spring2010/2_OCN621_Sediments_Handout.pdf

 

[bioload]

Okay.....Finally got my hands on a Milwaukee SMS-125 today. At first the ORP of my tank (about a month old) was all over the place with swings from 85-400.

Started to settle down and was moving from 95-110, then it was stable at 111. Over the past 1/2hour it has increased by 1 every few minutes or so to 123.

Is this normal....I've read that it there is a "break-in" period.....What is breaking in?

 

[Boomer]

It will take about two weeks for break-in, then post back

 

[bioload]

It will take about two weeks for break-in, then post back

Went back and did a bit more digging on redox measurements. I was unable to find anything that would explain the concept of breaking in with regards to redox measurements. From my limited understanding are we not just measuring the voltage difference between two electrodes? What would need to change over time in order to get an accurate reading?

 

[Randy Holmes-Farley]

I discuss equilibration of redox probes here:

ORP and the Reef Aquarium
http://www.reefkeeping.com/issues/2003-12/rhf/feature/index.php

from it:

Reasons That ORP Measurement May Be Inaccurate

There are a variety of reasons that ORP values taken in aquaria may be inaccurate. The primary one is that the platinum electrode may become fouled in a variety of ways. For example, it is expected that the platinum will get a coating of materials on it that can include oxygen, sulfur compounds, and organics. All of these will impact absolute ORP values. If an electrode is moved from a fluid containing one set of these compounds that bind to the electrode surface to a different fluid with a different set, the ORP may take a long time, even hours, to stabilize.

Additionally, as soon as bacteria grow on it, they can lower ORP be reducing the local O2 concentration. Likewise, if the probe is in a lit area, algae can coat it and release O2 locally onto the platinum. The end result is a greatly increased ORP. Occasional cleaning eliminates some of these concerns, but because of these issues, one should not put too much emphasis on the precise ORP readings in any given aquarium.

 

[bioload]

Thanks again

Looks like the "battle" has stabilized at 160mV +/- 10mV. What that means, is it normal......still reading up. I guess one can conclude that I either have a less oxidizers than "normal" or more reducers.....just want to make sure the probe is working properly

But back to what I originally wanted to use the probe for.....If I were to now place it in an anaerobic zone (plenum under DSB), would the readings take just as long to stabilize?

I think Boomer had mentioned somewhere that these probes have a tendency of developing a "memory"......I'm beginning to think I might just have to get a DO meter.

 

[Randy Holmes-Farley]

ORP is the tool most scientists use to understand the chemistry of sediment beds, not dissolved O2.

What is the goal of such measurements?

This has more info on sediments and redox:

Hydrogen Sulfide and the Reef Aquarium
http://reefkeeping.com/issues/2005-12/rhf/index.php

 

[bioload]

I'm currently setting up a remote deep sand bed and looking for a way to determine if it is anaerobic. On the mobile at the moment but will give more details when I get to a real keyboard.

 

[Boomer]

Looks like the "battle" has stabilized at 160mV +/- 10mV. What that means, is it normal......still reading up.

Pretty low but should come up into the 200 at least in the tank. A well run reef tank can easily be in the very high 300 without ozone.

think Boomer had mentioned somewhere that these probes have a tendency of developing a "memory"

When ORP or pH probes go bad at times they get a locked in memory kind'a. Meaning, the reading stays the same no matter where you out it.

 

[bioload]

Here are a bit more details regarding my tank at the moment.

Flow Through DSB

As mentioned I would like to add a remote deep sand bed to the tank in an attempt to lower nitrates. From what I understand the low or no oxygen zones of a sand bed are required for de-nitrification to occur. Since I already have access to an ORP meter I would like to use that as an indication of conditions within the sand bed (is it anaerobic?). Rather that placing the probe directly into the sand I'm creating a void within the sand bed where water may be removed and tested.

I've seen many applications of deep sand beds, however, none first hand so I tend to question the results. Rather than taking the wait and see approach I would like to know what is occurring within the bed and if conditions are right.

I'll be posting more details regarding the set up of the DSB in the thread above.

I hope this makes sense.

 

[Randy Holmes-Farley]

If that is the goal, then the ORP meter is a suitable thing to use to monitor the sand, but the ORP may vary with depth.

 

[bioload]

but the ORP may vary with depth.

Another good thing to find out. How deep does a sand bed really need to be? Might have to pick up some calibration fluid to confirm my meter is accurate. Are there any standards you recommend I use?

 

[Randy Holmes-Farley]

Yes, I discuss ORP standards here:

ORP and the Reef Aquarium
http://www.reefkeeping.com/issues/2003-12/rhf/feature/index.php

There are several hobby ones now, including one from Pinpoint (American Marine).