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Automating Reef Tank pH Alkalinity Calcium and Magnesium Control
Last updated on August 30th, 2023
Automated Reef Tank
This article about automating the pH, Alkalinity, Calcium, and Magnesium control is part of a series of articles I am writing about how to automate a reef tank. In theory, a fully automated reef tank would require you to do absolutely nothing. In reality, any of us that own an aquarium know that is unlikely at best but essentially not possible. That being said, what if we automated 80% or more of the reef tank? Then you would only need to worry about things like cleaning pumps, saving coral that fell over, and other minor jobs.
While each part of automating a reef tank comes with different layers of cost and difficulty, you will need to decide how far you want to take the control. A perfectly controlled environment is expensive and complicated, but one that hits 80-90% may be far less! It's really up to you to decide how far you want to go and how much you're willing to do yourself.
You Need a Reef Tank Controller
You will need a reef tank controller to control and measure ph, alkalinity, calcium, and magnesium. You don't actually need to control all of these parameters. In fact, most people only control one or two of them and then do large additives as needed. Controlling all of these parameters will, however, help lock in your success with any coral that has a calcium skeleton.
Reef Tank pH Control Automation
Automating Reef Tank pH is a bit more complex than most reef tank parameters, and is directly affected by alkalinity and calcium chloride (the calcium part of 2-part). Because of the complexity of dosing to control pH, rather than repeat the details, I am going to send you to the article pH Control with Kalkwasser Dosing.
Kalwasser - Calcium Hydroxide - Summary for pH
Essentially, when you increase alkalinity, you also increase pH. However, the amount of CO2 in the tank, and air around the tank, will push the pH up or down. In an ideal world, you would have windows open and nearly no CO2. In reality, most aquariums are either in a basement where CO2 from furnaces or people builds up, or in the living space where people and pets are breathing, creating CO2.
Kalkwasser is a chemical that reacts with CO2 and raises alkalinity, calcium, and pH! It's essentially a 1-Part solution that fixes almost everything. The downside is that it is so high in pH that it causes plastics to become brittle and should only be handled with gloves. Keep this in mind when you work with kalkwasser. Additionally, if you are using kalkwasser to control alkalinity, it will take a LOT of kalkwasser. It may be the same or more than the evaporation rate of your reef tank. Because of this, for alkalinity you make want to supplement with additional methods we will talk about later.
Controlling pH in the Reef Tank
The reason pH control is difficult is because you're not only measuring pH, but you need to make sure your alkalinity doesn't get too high either. So now you're balancing two parameters, which is part of the reason why most people don't try to control pH. Most people control alkalinity out of tradition and then complain about low pH. You can have the best of both worlds!
Enough about all of that, here is how you control pH in the reef tank. You will need to set up a dosing pump for kalkwasser and the amount to dose starts with about 2x the amount of water your tank evaporates in a day. You will dose that over an entire day.
Next, you will have your reef controller turn the dosing pump OFF when ph greater than the pH you'd like to target. I recommended turning off the dosing at 8.25 personally. But there is a second part to this. You will also want to set a maximum alkalinity.
If your pH maintains stable, you will see alkalinity rise when windows are closed, and/or there are more people in the room. You will also see alkalinity drop when there is less CO2 in the air, such as when the windows are open. So you will really want to set an alkalinity max to prevent the water from becoming to caustic, or even just being unstable. You will also want to turn off the dosing pump when alkalinity is at or above this max number you set. I recommended turning off the dosing pump if the alkalinity hits 11 dKh.
Example of pH Control
While I don't have a full variety of controllers to give examples, here is an example for the Neptune Apex:
If pH > 8.25 Then OFF
If Alkx7 > 11.00 Then OFF
Almost too easy, right!? The downside to this is that you need to monitor both pH and Alkalinity. If your controller doesn't support alkalinity measuring yet, then you will need to do that part manually. Measuring once or twice a day and turning the pump off if alkalinity is too high. If your controller does not support both alkalinity and pH monitoring, DO NOT try to automate pH Control. You'll miss a measurement and coral will likely die.
Controlling Alkalinity in the Reef Tank
While I encourage pH control, that isn't what most reefers like. If you are going to automate the control of alkalinity, you will still need to have a reef tank controller that can monitor alkalinity. That said, you have more options for chemicals to dose. You can use kalkwasser, which is still my preference, or you can utilize soda ash, or other alkalinity buffers. Additionally, you could use a calcium reactor to maintain alkalinity and calcium.
For the alkalinity control, figure out your typical alkalinity consumption. If you don't know how to do this, read Determining Alkalinity Consumption to find out. Keep in mind, this may change with time, CO2 concentration, etc. So you will want to verify this weekly to monthly.
If your controller measures alkalinity two or more times per day, set your dosing pump to add the amount of alkalinity buffer needed to meet that demand, plus about 10% (multiply by 1.1). If alkalinity is only measured once per day, only set the dosing to the exact amount needed. To find out how much to dose, you can use the Reef Stable Dosing Calculator.
Now, much like the pH control above, set the dosing pump to turn off if the alkalinity is above a target area. If you're controlling alkalinity, I recommended about 8.5dKh.
If Alkx7 > 8.5 Then OFF
If pH > 8.4 Then OFF
You'll notice I left the pH line in there as well. That's because alkalinity buffers increase pH too and you don't want pH to get above 8.4 or you will risk your coral health again. If you don't have pH monitoring though, this can be left out. Just keep a close eye on this!
Combining Alkalinity and pH Control
Just to clarify, these two methods are NOT mutually exclusive. You CAN and SHOULD do both! Personally, I use kalkwasser to maintain pH, and then added 2-part dosing to help maintain alkalinity at my desired 8.5 dKh. You'll notice that kalkwasser turns off at the extreme high side of alkalinity, and 2-part turns off on the extreme side of pH. This allows the main drivers for these to be that kalkwasser controls pH and 2-part controls alkalinity, but that they both have safety measures in case things get out of control. Make sure to change these guard rails to safe numbers for your reef!
Controlling Calcium and Magnesium in the Reef Tank
Calcium and Magnesium control in the reef tank are nearly as simple as it gets. The same way that you Determining Alkalinity Consumption, you can get calcium and magnesium usage.
For dosing, If your controller measures twice per day, I would just set the amount to 1.25x your daily usage, and then add the control below. If it only measures once per day, I would set the amount dosed to 1x the daily usage.
Calcium
If Cax7 > 420 Then OFF
Magnesium
If Mgx7 > 1350 Then OFF
More Information About Alkalinity, Calcium, and Magnesium in Reef Tanks
If you're looking for more information about what alkalinity, calcium, and magnesium do in a reef tank, and how they interact, I have an article that explains this in detail, Calcium, Alkalinity and Magnesium in Reef Tanks.
Conclusion
While not overly difficult, automating control of pH, alkalinity, calcium, and magnesium in your reef tank will greatly simplify your life. This will reduce the most frequent reef tank tests that you would need to do, as well as the most common manual dosing. The stability of these parameters will also improve coral health and growth! While there may be an up-front cost, this automation will save you a lot of money over time preventing coral losses!
Recommended Reading:
- pH Control with Kalkwasser Dosing
- Calcium, Alkalinity and Magnesium in Reef Tanks
- Determining Alkalinity Consumption
About the Author
John Krenzer
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!
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