Hydroponic ORP Management

Hydroponic ORP Management

Controlling & Monitoring ORP in Crops


Hydroponic ORP management gives growers the ability to observe and maintain a relative measure of the “health” of hydroponic nutrient solutions to grow crops. Managing ORP levels is especially effective in recirculating water culture systems like RDWC. ORP readings from monitoring devices are given as mV (millivolts).  The cost of the devices is inline with pH or EC monitors, etc–you can spend a modest amount for relative accuracy or invest more for more accurate readings, a range of features and a longer service life. ORP monitors and controllers look and work in a similar fashion too to EC & pH monitors and may require occasional calibration.

Healthy nutrient solutions produce excellent crops in hydroponic systems; maintaining healthy ORP levels are key.

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–not to worry, it would take some effort to overshoot the optimal working range for hydroponic solutions, especially since ORP levels can drop quickly if not supplemented with regularity.

If ORP readings of recirculating hydroponic nutrient solutions are low, for example below 250 mV, it maybe an indication that there is a problem with hydroponic crop health or may soon be. In an actively recirculating reservoir or hydroponic system with good aeration and optimal temperatures, the ORP level is likely to be +250 mV without supplementation. However, if there is any stress on the system or crop–which in the real world happens, the ORP value can drop below the minimal recommended value. When the ORP is below optimal for time, crop infections can occur and nutrient absorption rates may not be at full potential.

ORP Management

For good hydroponic ORP management practices it is recommended to supplement ORP values based on real time or at least daily ORP monitoring and checks–additionally, it pays to keep an eye on the ORP values of your source water, purified water and sored water. Healthy water is foundational for healthy plants–as well as a healthy bottom line for your growing investments.

As mentioned earlier, a variety electronic monitoring and controller devices for raising ORP are available to growers. A monitor will simply tell you what your ORP values are when measured, constant or as a hand held device for manual checks. A controller will allow the grower to enter an ORP set point value and when the value drops below this set point the device will trigger an outlet. Ozone (O3) may be added to the solution via venturi corona discharge or ORP raising additives such as hypochlorous acid (ClearLine or UC Roots) may be injected into the solution when triggered by the monitor.

Clear Line

Ozone VS Hypochlorous Acid

Ozone is a volatile molecule that oxidizes impurities.  Basically, as O3 it is unstable–the extra oxygen molecule wants to jump off onto another particle.  The result is O2 as a byproduct, and the neutralization of unwanted organisms such as fungi, bacteria, protozoa, etc. While effective at raising ORP, and overshoot or malfunction can be costly–and over abundance of O3 at a prolonged period can have disastrous effects on crops; essentially Ozone poisoning.

Hypchlorous acid raises ORP values and also offers additional benefits including reducing salt build up in hydroponic systems. Adding hypochlorous acid using peristaltic pumps with limiters or with visual checks makes it easier to prevent any potential harm in the event of an ORP monitor or controller malfunctioning or false reading. A grower will recognize how much is typically added to the system daily while with ozone this could be difficult to determine.

Adding hypochlorous acid manually to raise ORP is easy, cost effective and safe. Following label directions, many growers find it easy to add to the system daily, whether using a simple Add-Back adapter in recirculating RDWC systems or by pouring directly into water storage tanks, reservoirs, growing systems ,etc.

In conventional fertigation systems, besides for raising ORP, hypochlorous is an excellent addition to prevent scale and biofilms for better root health and drip irrigation system management. It can be added directly into the reservoir or ideally, injected into irrigation lines with a proportioner system when the system is active.

Practical ORP Management

Check and record recirculating systems, reservoir, RO water storage tanks and source water ORP values–keep a daily log.

Add hypchlorous acid as recommended by label. This may be performed manually or automatically–check values after adding to ensure ORP is between 250-400 mV.

Look for trends where ORP may be below optimal–are there seasonal issues with source water, for example?  What about RO systems–a decline in ORP may indicate that filters, membranes, injectors, etc may be in need of replacement or cleaning and maintenance.

If using peristaltic pumps or injector proprtioners note daily how much has hypochlorous acid has been delivered–has there been an increase or decrease? If there are drastic differences inspect dosing equipment to make sure that it is functioning correctly–if it is, inspect the crop for signs of stresses, ie infection.