Lets talk ORP

[Noahsnana]

Tell an novice what this is ...increase my knowledge

What is it?
How does it effect water quality?
What levels are desired?
How do you use an ORP Meter?

[Thomas T]

What is ORP?
ORP is a term used frequently in the water treatment & food processing industry. ORP stands for Oxidation-Reduction Potential. So what is that? The best definition I can give is that “ORP is a measure of the cleanliness of the water & its ability to break down contaminants”. It has a range of –2,000 to + 2,000 and units are in “mV” (millivolts). Since ozone is an oxidizer, we are only concerned with positive ORP levels (above 0 mV).

ORP Level (mV)
Application

0-150
No practical use

150-250
Aquaculture

250-350
Cooling Towers

400-475
Swimming pools

450-600
Hot Tubs

600
Water Disinfection *

800
Water Sterilization **

ORP sensors work by measuring the dissolved oxygen. More contaminants in the water result in less dissolved oxygen because the organics are consuming the oxygen and therefore, the lower the ORP level. The higher the ORP level, the more ability the water has to destroy foreign contaminants such as microbes, or carbon based contaminants. The chart on the left identifies ORP levels for various applications.



ORP level can also be viewed as the level of bacterial activity of the water because a direct link occurs between ORP level and Coliform count in water. The chart to the right lists ORP levels and relative Coliform counts.


200 mV 300 Coliform count in 100 ml of water
300 mV 36 Coliform count in 100 ml of water
400mV 3 Coliform count in 100 ml of water
600mV 0 Coliform count in 100 ml of water



How does an ORP meter work?

An ORP meter measures very small voltages generated with a probe placed in ozonated water. The electrode is made of platinum or gold, which reversibly looses its electrons to the oxidizer. A voltage is generated which is compared to a silver (reference) electrode in a silver salt solution, similar to a pH probe. The more oxidizer available, the greater the voltage difference between the solutions.


Disadvantages
ORP cannot be used as a direct indicator of dissolved ozone residual, except in very clean water applications.

Advantages
ORP is a convenient measure of ozone’s ability to perform a chemical task. ORP is valid over a wide pH range, and ORP probes are rugged enough to be place into processes for in-line measurement. The probes can withstand process pressures in excess of 30 PSI.

ORP and Ozone
In a clean water system, using ORP to measure the dissolved ozone status works well. In our experience, however, even the strong oxidizing power of ozone in moderate turbidity (cloudiness) systems can result in ORP values far below expected and even negative (reducing) values. In general, monitoring ozone with ORP at the generator source works well but measuring dirty water becomes unreliable. Ozone detection kits are available and work well at the limit of approved concentrations for your application.

[Noahsnana]

What about for normal pond usage? Can we elaborate?

[Thomas T]

How does it effect water quality?
What levels are desired?

At 250 - 300mV, the nutrients (DOC) as well as single cell algae are being oxidized into water & CO2. This is the one of the reasons why your water clear up so fast when PP is added to the water. In the nutshell, water quality improves. However above 500mV, you'll kill everything including fish & bio-filter.

How do you use an ORP Meter?
I have the probe & meter hardwired to my settling chamber on the Nexus. It monitors the water 24/7. The probe requires cleaning every 4-7 days using a wet tooth brush. See pics.

[CarolinaGirl]

Very informative Thomas, thanks! I like the idea of having the ORP meter mounted for constant use. Very fancy housing too, I might add . How long do the batteries last when you run it 24/7?

[Thomas T]

The battery is a single 9V cell and should last 3-4 months on continuous use. The plastic tuberware housing is velcro'ed to the Nexus.

TT

[MCA]

I think the values should be more for ~250 for the average pond. Over 300 for very good water quality, over 350 for fantastic water quality. I know who koi keeper who's pond water is near 400 and he does not use ozone or PP....just fantastic filteration and aeration.

I try to keep our pond in 300+ range...it aint always easy.

[Noahsnana]

Thanks for taking the trouble to post a pic to demonstrate application Thomas.

So the ORP meter is measuring Disolved Oxygen in the water... this replaces the kit test w/drops. How accurate are the meters... How offten are they calibrated or do you calibrate these meters?

[nicco]

Umm. Nope. ORP does not measure dissolved oxygen directly, nor is it a measure of dissolved oxygen content in the water. You use a DO meter to measure dissolved oxygen. ORP is a measure of the potential of the water to oxidize substances in it. To us this usually means the decay of waste products. How much potential the water has to carry out this decay is dependant on many things, dissolved oxygen, temperature, pH, amount of contaminants, the presence of other oxidative chemicals (such as chlorine or potassium permanganate) and so on.

The chances are that if you have a high value of ORP (say 300 and above) and you do not have any oxidative chemicals in the water then the water is probably quite clean. In this way, the value is being used as an indication of how well your filtration system is working and how healthy the water is.

Some folks clean and calibrate their meters very regularly. I find that mine only need calibration at most once a month. Once I left a probe in the pond for four months and it still calibrated correctly. Some meters cannot be calibrated.

[Thomas T]

The easiest way to build up your ORP to 300+ is installing a large trickle Tower or Bakki Shower like Carloskoi's. If you have a submerged medium filter system, it'll be tought to break the 300 mark without ozone or PP.

TT

[MCA]

http://www.koiclay.com/page6.htm

[Noahsnana]

Thank you nicco for politely correcting me I really appreciate it.

[Noahsnana]

http://www.koiclay.com/page6.htm

Thank you MCA explained everything.

Measure of pollution... boy was I going I the wrong direction.

[MCA]

You are welcome.


While we should all target our pond water to be around 400mv, the reality is most of us are doing good to be in the 300 range. But everyone should have water that greater than 200.

[Blammo]

You are welcome.


While we should all target our pond water to be around 400mv, the reality is most of us are doing good to be in the 300 range. But everyone should have water that greater than 200.

Right, Mike.
To elaborate..
ORP, if used at all, should be to get an AVERAGE measurement of water " quality"
This means measure a couple times a day over a MONTH to get an average.
Feeding, rain, water changes, leaves(leefz ?) in the pond all DRASTICALLY change ORP.

There are SOME who chase it hour by hour... Idiocy !

The meters best job is in doing "prolonged" PP treatments
I wont elaborate on "prolonged", at this time...

[Noahsnana]

Is there any other way to measure DOCs levels?

[Noahsnana]

Is there any other way to measure DOCs levels?

Anyone?

[allen42]

Thanks for starting this Thread Nana , I sho nuff learned something from this & now i want a ORP meter !!

[Noahsnana]

Me too Allen. Just curious as too any other way to measure the pollutants on the water beside sight and ORP.

[koiingaround]

Me too Allen. Just curious as too any other way to measure the pollutants on the water beside sight and ORP.

I have been wanting one for a year now...
hehehe but there are soooo many other things that are always needed too...sigh...