ORP: Potentially The Most Influencial Parameter

ORP: Oxygen Redox Potential, Potentially the Most Influential Parameter Period

ORP, or Oxidation-Reduction Potential, is one of the most important parameters in any marine tank. ORP is the measure of electrical conductivity related to your systems potential to recycle waste and other organics. The reading is based off the charge given off by the particles in the water. You should have a fairly vague understanding of ions and how their particles can jump to other particles, but if your education system skipped that class (or you slept through it), here is a very short refresher.

REDOX a.k.a. Oxidation-Reduction is when Oxidizers and Reducers meet and transfer electrons, which carry charges of (-1). When molecules meet other molecules with less attraction to these electrons it causes them to hop to the greater molecule, thus REDUCING the original molecule. When one molecule (Oxidizer) gains electrons it actually REDUCES in charge due to the negative charge of the electron. The REDUCER (which lost the electron) then becomes an Oxidizer with a higher charge. This can happen rapidly or can take thousands of years to complete reactions and exchanges depending on the particular particles at hand. It is a bit confusing, and somewhat backwards, but science is like that sometimes. Do you HAVE to know this stuff to be able to control ORP? No, but it really does help to have an understanding.

ORP in the Aquarium:

Molecules are at constant battle with each other. They are continuously taking or giving electrons to and from one another. This puts an actual electrical current across the cells which can be measured in Millivolts, or mV. The thing ORP meters test is the intensity of said current. Originally, ORP was supposed to be the measurement of water purity but has more recently been theorized as the potential for the water to reuse particulate matter such as food, waste, or any other dead organisms.

ORP is certainly a broad factor. The point of testing is to give an idea of the total collection of particles (assuming they are all working at an equilibrium) and their ability to break down things. The pH of your tank can alter the ORP. ORP is also thought to fluctuate with the pH, so at night you will get a different reading than in the day. Probes can also get buildup of algae and other particulates that will also effect the readings of your water.

 Testing the Waters:

First of all, ORP meters need calibrated according to their instructions with calibration solution. Just read the directions, it is very easy. Due to the varying reaction times, you must take tests over longer periods of time, and if you have a controller with probes or aquarium app on your phone you can see the progress of you ORP readings on a handy graph and really understand what your tank is doing.

ORP readers are not exact on their readings, but being consistently off is good. The thing we are looking for is stability and consistency. Due to the inaccuracy of test kits, the Absolute Value of the ORP is not as important as the fluctuations between the initial readings. We are only tracking changes in readings, the actual numbers are somewhat irrelevant aside from finding the range between them. If your first test reads 350 and your second test reads 305 than than the difference, 45, is what we are focusing on.

ORP readers have the capability to test for death! Have you ever had a fish disappear from your tank only to find a nice patch of Cyanobacteria or algae? When monitoring for ORP and a fish dies, within hours the readings will drop. This alarms us to search for any carcass that could be rotting, preventing any outbreaks or parameter peaks.

ORP meters are also used when dosing or using oxidizing products like Hydrogen Peroxide or Ozone. Ozone is an extreme oxidizer and is used in part to raise ORP levels along with sterilize water. Using the meter to monitor ORP while dosing these types of things can help not to shock your tank. Rapidly increasing ORP even to healthy levels is very harmful. Slow changes (like all things reef) are very important.

Target Range:

The ocean is unbelievably stable, yet the ORP level ranges from -384mV to 450mV. That is a huge range of 834mV! Keep in mind these readings are not from one spot but from different locations in the ocean. The Reefs are generally in the range of 300-450mV, which is much more stable. In our tanks we try to aim between 200-450mV. Quite a broad range in terms of units, but when you consider the 834mV range our oceans have it is actually quite stable. In fact, ORP is one of the few parameters that are more stable in an aquarium than the ocean! The suggested range is not scientifically produced, nor an exact recommendation of a range for your tank. Every aquarium is different and reacts differently to ORP readings of varying degrees. Trial and error are truly the only way to get an exact ORP range that is good for your tank. Once you pinpoint the sweet spot you can use the methods above to increase or decrease levels when needed.

ORP is extremely important to understand and quite remarkably one of the most important parameters you can test for. It is wise to get a monitor for long term data recording. The good thing is that it is extremely easy to manipulate with the knowledge we have today. Do the right thing and test it today!

More Forum ORP Discussion Here