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The Secret to Reef Tank pH
Last updated on November 17th, 2023
Reef Tank pH
Reef Tank pH is one of the most important parameters for coral growth. Yet most of the time, we're told not to "chase numbers". This is because many people add chemicals and disturb the chemistry of their reef tank trying to get pH to 8.3. I'm going to show you how to increase your pH without adding a bunch of chemicals to your reef tank.
By implementing just one or two of these tricks, you should see a natural increase in your reef tank, and maybe even see more stability. At the time of writing this, I am seeing my pH drop by 0.1 overnight and back up in the morning. I would prefer to make that change even smaller an will update this article to give you more information as I learn it.
I'll warn you, there is a bit of chemistry involved in this article to understand reef tank pH. If you don't care about the science, just read the first part and either watch the video or skip to the bottom for solutions. (Don't worry, I get it).
What is pH?
PH stands for "potential of hydrogen" or "power of hydrogen". Reef Tank pH measures the amount of hydrogen in your reef tank. The main use of pH is to determine the acidity of a solution, in this case, your reef tank.
Okay... You can say it... NEEEERRRRRDDDDD....
I know that last part was a bit nerdy. That's what a lot of this hobby is though. Science. So if you're looking to grow coral to the best of your ability, get ready for some chemistry.
Why is Reef Tank pHs Important?
The short answer, pH is one of the most important parameters for keeping coral. If your reef tank pH is too low, the water becomes acidic and coral may grow slower than it should, or even die. This is the simple explanation for why Reef Tank pH is important.
Dropping some Science
Now for you science people out there. I should start by saying I was AWEFUL at both High-School and College Chemistry. So bare with me as I try to explain the importance of Reef Tank pH.
Reef Tank pH - How do Corals Grow?
Corals, especially SPS and LPS coral, grow by expanding their skeletons. These coral skeletons are made from Calcium Carbonate. The coral pulls both Carbon and Carbonate from the water, combine them to form Calcium Carbonate, and expand their skeletons.
Okay. So, Calcium + Carbonate = Calcium Carbonate => Which makes coral grow. So far, so good.
Reef Tank pH - Carbonate vs Bicarbonate
The next part of the chemistry lesson is that there is generally far more "bicarbonate" in the reef tank than "carbonate". What's the difference you ask? No? Well I did!
Bicarbonate is Carbonate with an extra Hydrogen atom. That's it. That extra hydrogen atom causes some problems for Reef Tank pH. When coral consumes bicarbonate, it has to remove the hydrogen atom before combining the calcium. This hydrogen atom then stays near the coral skeleton. Remember the beginning where I told you what Reef Tank pH means? More hydrogen, lower pH, less coral growth and potentially death. So as the hydrogen atom sits near the coral, it decreases the pH within and around the coral.
Does your head hurt yet? Cause mine does! Were almost there!.
So now the coral is stuck with this hydrogen atom lowering the pH and killing it. How does the coral get rid of the hydrogen atom? This part is simple. The coral takes the hydrogen and pushes it somewhere else.
The less hydrogen in the water, the easier it is for the coral to shed the hydrogen atom. Meaning the Reef Tank pH should be higher (less hydrogen) in order to help corals grow.
You made it through the first section of Reef Tank pH Chemistry! If you didn't quite follow, don't worry. There won't be a test. If you're like me though, you may need a video with more or better pictures to understand the topic. So here is a video from Bulk Reef Supply covering Reef Tank pH.
How To Increase Reef Tank pH
To increase Reef Tank pH, you first need to identify the reason why the Reef Tank pH is low. Generally low Reef Tank pH comes from excess CO2.
Yeah, here's a bit more science. When CO2 mixes with water H2O, it creates carbonic acid (H2CO3). Why is this important? Because acid lowers reef tank pH.
So to recap, CO2 + Water = Carbonic acid, which lowers the Reef Tank pH.
Now that we made it through that Chemistry lesson, how do we increase pH? There are a few ways. Most of these will be a recap from the video above.
More Air in the Reef Tank
The first, and likely easiest way to raise reef tank ph is to increase the air in the reef tank. As fish and other creatures breath, CO2 is expelled just like when humans and animals breath. If there isn't enough water movement at the surface of the reef tank, or if the protein skimmer is not large enough, there may not be enough air exchange to remove the CO2 and bring in oxygen.
There are a couple of ways to increase air exchange in the reef tank. The first is to increase your pumps' flow and aim them toward the top of the tank. This will cause turnover at the surface and increase gas exchange.
Another way is to bring in more air with your protein skimmer.
Finally, you could implement Micro Bubble Scrubbing. This forces air in all of your reef tank, increasing reef tank pH.
If any of these methods help raise your reef tank pH, then the problem you are facing is simply gas exchange and you now know how to fix it.
Less CO2 in the Air
If the problem wasn't fixed, or maybe reef tank pH is not quite where you'd like to see it, after better gas exchange, you may have too much CO2 in the room. CO2 is produced when you, or even your pets, breath. So how do you remove CO2 from the room? Open a window! Yeah, I know, not quite that simple. In the middle of hot summers or cold winters, opening the window may not make sense.
Another way of bringing fresh air in to your reef tank is to run an air line from your protein skimmer's air intake outside. This will force fresh air with lower CO2 levels rather than the air within your home. This is a common method of increasing your reef tank pH.
If you don't have a reasonable way of bringing fresh air in to your tank, you can reduce the CO2 and increase the reef tank pH using a CO2 Scrubber. This involves using a CO2 Scrubbing Reactor and CO2 absorbing media. To use the CO2 Scrubber, you will connect the scrubber to the air intake of your protein skimmer. This will raise your reef tank pH and you won't have to drill a hole outside! The reactor and media is actually quite affordable too. Before buying more equipment, it may be best to try the window or hose outside to ensure this is the cause of your low reef tank pH.
Other ways to Raise Reef Tank pH
There are some other ways that you can raise or stabilize reef tank pH. Some of these options are cheaper than others. I would encourage starting with the lower cost options first. It should be noted that these methods will likely not work as well as those mentioned above, but it may be just the little boost your reef tank pH needs to get closer to the 8.3 target.
Running Refugium at Night
When the reef tank's lights turn off, the corals and algae in the tank stop photosynthesis. Photosynthesis is part of the process of removing CO2 from your aquarium. If you monitor your reef tank pH using a controller like the Neptune Apex, you will likely see the pH lower at night. One way to help stabilize the reef tank pH is to turn your refugium's light on opposite your aquarium's light. This way, the macro algae in the refugium will begin to absorb CO2 during the photosynthetic process. This will help increase reef tank pH at night and help keep the pH stable.
Plants in the Room
Some people have had success by simply keeping plants in the same room as their tank. This is because plants absorb the CO2 from the air and produce oxygen. By reducing the CO2 in the room, it will be much like opening a window, providing fresh air. However, it is hard to know how many plants and what type you would need to achieve this. Regardless, it is worth a try!
Air Exchanger - Home HVAC Updates
Air exchangers are a large upgrade to your home HVAC system. It brings in fresh air from outside to enhance the air quality in your home. This can be quite costly however. If you are looking to add an air exchanger to your home HVAC system, look into the benefits in addition to raised reef tank pH.
This article has a lot of chemistry involved, but hopefully I was able to simplify it in a way everyone is able to understand. Reef tank pH is a key component for coral health and growth. Maintaining stable, as always, is the goal. The target value is to have a reef tank pH of 8.3 and most commonly hobbyists fall short. That is why most recommendations are focused on increasing the reef tank pH.
Though I believe you should not chase this "magical" number of 8.3, it is good try try to get close and maintain stable reef tank pH. I do not encourage using chemical additives or additional buffers to increase your pH as this can affect your alkalinity as well! Causing more harm than good.
Frequently Asked Questions:
How to raise reef tank pH?
Reef tank pH can be increased by making the water less acidic. Common ways to do this include reducing CO2 in the room by opening windows, or running the air intake line of the protein skimmer outside. There are chemical additives that raise reef tank pH as well, but many of these may affect your alkalinity levels as well.
How to lower reef tank pH?
To lower reef tank pH, you need to make the water more acidic. The most common way to do this is by dosing vinegar to the reef tank. You can reduce the reef tank pH by roughly 0.3 by adding 1 mL of distilled, white vinegar for each gallon of aquarium water.
What should reef tank pH be?
Saltwater aquariums generally have an acceptable pH range of 7.6 to 8.4. You should try to remain as stable as possible with one value. Reef tank pH should be a bit higher for coral growth and health. Ideally within a range of 8.0 to 8.4. The "golden target" for reef tank pH is 8.3.
About the Author
John is a Software Engineer with a passion for saltwater aquariums, as well as the founder and president of Reef Stable. He started in the aquarium hobby as a child with a 20 gallon freshwater aquarium. His interest in aquarium life grew and in 2008, John set up his first saltwater aquarium.
Today, John maintains an over 300 gallon reef tank system, consisting of a 120g reef and a 210g reef. These large tanks are contained within the same system, sharing a sump as a means to reduce total maintenance and increase total water volume.
John writes articles for the blog as a means to learn about more reef aquarium topics. These articles act as a reference for the readers as well as himself. John updates these articles frequently to provide additional information or make corrections as new information becomes available.
If you would like to request an article, tank tour article, or to collaborate, let me know via the Contact Me Page!