Because ORP is an important water parameter, there are many equipment products and chemicals out there that claim to control ORP levels.
Some people think that ORP levels in an aquarium have to do with the clarity or purity of the water, but this is not true. It is much more complicated than that. ORP allows you to assess a molecule’s ability to oxidize. This oxidation allows for the reduction of another molecule.
This article discusses ORP, what it is, what can cause it to increase or decrease, and how to keep the levels balanced in your tank.
What is ORP?
ORP refers to Oxidation Reduction Potential. In marine aquaria, it is a measure of the relative oxidizing power of the water. ORP has to do with the electrochemistry of natural water.
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ORP is a measure of the “battle” between oxidizers and reducers. If this battle ever ended, everything in your tank would die. If your ORP gets too high, it could kill all the bacteria in your tank.
Oxygen molecules fight for the oxidizers. Oxygen molecules get into your tank thanks to photosynthetic organisms such as coral and algae. Other oxidizing fighters include O3, H2O2, 3O2, and O2, as well as Cl2 and NH2CL. Anions and metals also help the oxidizing side.
The reducers are on the other side of the battle. They are less numerous but larger in size. Their goal is to get rid of electrons. Antioxidant vitamins are reducing agents as well as inorganic compounds such as ammonia, sulfide, and iodide.
Reducers get added to your tank from fish food, the breakdown of dead organisms, waste products, and other additives you put in your tank. The surface of most organisms in your tank are reducers as well.
ORP is the measure of the fighting ability of both the oxidizers and the reducers. You want this to remain balanced, not letting either side win the battle. The exact value of ORP is a constantly varying number. Adding oxidizers will increase the ORP, and adding organic molecules as reducers will decrease your ORP levels.
What is an average ORP level?
A typical aquarium ORP reading will be around 59 mV/pH unit. It should fluctuate on either side of this number. The recommended range is not exact because each aquarium is different and reacts differently to ORP readings.
To understand ORP levels, think of pH as a measure of hydrogen ions, which are on the oxidizing side.
Why measure ORP?
If the oxidizers win, organic molecules will be burned away. If the reducers win, there would be little oxygen left, and toxic hydrogen sulfide will take over. Either way, your tank will be a disaster.
That is why you want to keep ORP levels balanced as best you can to keep a steady middle ground for both sides. You don’t want to let either side win the battle.
The ocean has an ORP range of 300-450 mV. You can successfully keep an aquarium at this range, but as long as your tank’s ORP levels are between 200 and 500 mV, you are in good shape.
ORP is used to monitor if anything unusual happens in your aquarium. A sudden drop or increase indicates that one side is winning the battle. This could be caused by a lot of things. Keeping an eye on ORP levels in your tank can help you figure out if something in your tank needs your attention.
You should not overemphasize ORP readings. This level is susceptible to errors. The best way to use ORP measures is to determine if there is a problem in your tank that you can’t figure out otherwise.
What causes high ORP in a reef tank?
In general, the higher your ORP levels, the healthier your tank is. But you do not want it to be too high. If your levels are over 500 mV, you probably need to take action to decrease your ORP levels.
When the ORP level in your tank is high, it means there is a lot of oxygen present in the water. Your tank’s oxygen levels may be high because you added too much Ozone, which is an extreme oxidizer.
It could also be that your ORP levels are not high at all. It could be an inaccurate reading. Make sure there is no algae on your ORP probe. Next, try calibrating your probe. If this does not work, it could be that you have a bad probe.
If you want to decrease ORP levels, you can add more organic molecules to your tank.
What causes low ORP in a reef tank?
Low ORP in a reef tank could be caused by a sudden gush of organic molecules that have been released from a dead organism. If you have had a fish disappear, you can find out if it is dead by an ORP reading.
It could also be that the oxygen supply is not keeping up with demand. Ozone is an extreme oxidizer that you can add to your tank to raise ORP levels.
When adding products to your tank to raise ORP levels, remember to monitor the ORP levels as you add so as not to shock your tank.
How to keep ORP levels balanced
It is challenging to keep ORP levels balanced because it is such a complicated concept. For example, your tank’s pH levels may be affecting your ORP levels. Or it may be your ORP levels that are affecting your pH levels.
This is why you should not focus solely on ORP levels to determine how healthy your aquarium is. As long as your ORP is between 200 and 500, focus on your other chemical levels. Use the ORP to determine if something is wrong in your tank that you don’t know the cause of.
ORP is not a measure of water purity. It is a measure of the potential of water to reuse food, waste, and dead organisms.
ORP is a broad factor when it comes to measuring the health of your tank. Many factors can affect your tank’s ORP readings. For example, you must calibrate your ORP meters.
Testing for ORP levels can help you determine if something is wrong in your tank, but the readings should not be taken as 100% accurate. Also, because the recommended range is so large, you don’t have to worry about pinpointing a specific measure and keeping it steady.
Too high ORP readings may mean there is a lot of oxygen present in the water. Too low readings may mean that one of your fish or other organisms has died and is in the process of decay.