Do you track ORP in the root zone? This can be raised with aeration, ozone, or a UV sterilizer to raise the water quality and prevent pathogens like pythium and fusarium. Floraflex has a good article about ORP in the root zone:
Common meter brands for ORP are Milwaukee and Hanna, although there are several options at all price ranges. Tracking ORP is another important metric with cultivation and plant health. I look forward to hearing how ORP affects your cultivation inputs.
I’m glad you started the thread.
I don’t have any experience with ORP yet.
I first heard of it when reading the manual for a “multi-parameter” meter I was going to buy, and I did buy. The Apera SX823-B (Same as the PC850) does pH, EC, Temp, but also mentioned that an ORP sensor probe could be connected where the pH probe normally connects, and that the meter can read ORP as well. I thought that was a bonus that I might use in the future, after quickly looking up what the heck it was. I think I skimmed an article by @danielfp about orp, too.
I was “shopping” around looking for sensor probes, and full orp meters.
I found Milwaukee has some models in a “decent” price range. A monitor, and a cheap looking controller to.
Hannah’s look too expensive for me. Even their ORP pen is well over $200 cad (direct on their site. I duno about retail.)
Atlas Scientific has some nice looking options (they don’t really make end user products though. But their new “EZO complete” products change that to a degree. And I was just told they have an “EZO switch” in the works that would allow easy connecting of output devices to the setup, so you can “control” what you’re monitoring more easily (without coding).
Apera makes an ORP probe for the multi-meter I have. It’s $108 cad+tx. They also make a stand-alone ORP pen. It’s $160. These are amazon.ca prices.
Another brand or two, some sounded quality, others were $30 amazon.ca junk - not a lot of that surprisingly.
Seems like around $200 cad minimum.
Edit: Also, I’m not sure of the things I need to know about these devices before buying. What features to look for and avoid. Does temp. affect ORP, does it need temp. compensation, does it need a built in sensor for that? pH affects ORP (is my understanding), so does it need to be accompanied by a pH probe to account for this - does it need to account for this and have a reference of what the pH is? Double junction, I guess (cause why not?), haha.
–Another thought, I heard that “reefers”/aquarium folks might know about ORP as they use this as well.
There’s some good stuff in this article, I think. https://www.yokogawa.com/ca/library/resources/white-papers/basics-of-orp/
Some of the really technical stuff I only skimmed. But I took some quotes/notes. If this is useful, cool. If not, I’ll delete, if it’s just clutter.
“ORP is measured in milivolts (mV), with no correction for solution temperature.”
“When measuring ORP an important feature to remember is that unlike pH, temperature compensation is not normally used for ORP measurements.”
“An ORP measuring electrode can either be a separate electrode (as seen in Figure 3.4a), a combination ORP/Reference electrode (as seen in Figure 3.4b), or a combination ORP/pH measuring electrode (as seen in Figure 3.4c). The choice depends on the application as well as customer installation requirements.”
"One drawback however, is that pH changes also affect the oxidizing potential of the available chlorine and the resultant ORP value.
Below a value of 1.9 pH, chlorine exists as a diatomic molecule (Cl2) in water. As the pH increases above 1.9, chlorine oxidizes water to produce HOCl and the ORP millivolt reading will go down. As the pH value continues to increase HOCl further dissociates into OCl- above a pH of 7.3."
"HOCl being more active that OCl- has a higher ORP value. So, as the pH increases, an ORP sensor detects a decrease in value which reflecting the decrease in HOCl. Therefore, if we were using ORP to monitor the diatomic Cl2 level, we would have a large mV reading to start with, but as it oxidizes with water reacting with the Calcium Thiosulfite to form a salt, the mV reading would decrease.
Since ORP varies with pH changes, as well as changes in the chlorine levels, we must compensate for the effects of any pH changes. This can be done by measuring the pH and ORP independent of one another and then calculating the effect of the pH change on the ORP using formulas and graphs. A simpler and more direct method is to compensate for the pH changes by replacing the standard Ag/AgCl reference electrode normally used with a pH measuring electrode. This is known as pH Compensated ORP (rH).
Since the pH measuring electrode output changes as the pH of the process changes it acts as a moving reference effectively cancelling out any change in pH and leaving only the mV value which is due to changes in diatomic chlorine (Cl2) levels."
Yes we use inline UV Sterilizer on the batch tanks. First time using them but I have no issues. Thought it was overkill at first but now I would not sleep at night without them.
A good hydroponic ORP value range to maintain for optimal hydroponic crop health is typically 300-400 mV. Going +450 mV can be counter productive and at prolonged periods can damage roots in some instances . . .