ACI Aquaculture's pH Control with Kalkwasser Dosing
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ACI Aquaculture's pH Control with Kalkwasser Dosing

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Last updated on November 17th, 2023


ACI Aquaculture's pH Control with Kalkwasser Dosing

Stable pH Control at ACI Aquaculture

In roughly late 2020, I wrote an article about stabilizing pH using kalkwasser. The conclusion of that article was that you could not maintain a consistent pH and alkalinity using only kalkwasser. As it turns out, this was only partially true! After Chris Meckley has been talking about pH stabilization for a couple years and proven the theory, I decided to re-write this article now that I have learned more about how pH control, and kalkwasser chemistry works!

At ACI Aquaculture, Chris Meckley has implemented a new way of dosing that breaks the known rules of reefing entirely! Instead of maintaining balanced alkalinity, Chris focuses on keeping a balanced pH. While not ignoring alkalinity, this method has been putting alkalinity second, while still ensuring some level of stability.

While there seems to be little scientific evidence one way or the other (like most things in the hobby), Chris is having great success at ACI Aquaculture with this pH control method. While he uses different, more potent methods as well, Chris talks about using Kalkwasser to maintain pH both stable, and closer to natural sea water levels.

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This topic is HIGHLY controversial (especially at the moment), and as such, this article should be treated as more of an informational resource for what this method is and why it is considered.

Like anything else in this hobby, use this information at your own risk. We know that large swings of alkalinity have been linked to coral death. While a few Reef Keepers are starting to try this method, it has not been tested long term nor generally accepted as the "rule" for reef keeping/dosing. Use your best judgement and be careful to minimize swings in all parameters to optimize your reef and not cause coral death.

Reef Stable, ACI Aquaculture, and Any/Every other person referenced in articles or videos are not responsible if you try anything mentioned.

The Theory of pH Stabilization

This theory focuses on stabilizing pH at or near the 8.3 found in natural sea water. Most home reef tanks commonly see pH as low as 7.8, which is likely one of thr main reasons for difficulty with growing coral! The main reason for the low pH is CO2 causing carbonic acid.

When CO2 enters the reef from the surrounding air, as well as the fish exhaling, it mixes with the water (H2O) and becomes carbonic acid (H2CO3). Being an acid, the pH then drops. So, how do we improve the pH? We either prevent CO2 from becoming carbonic acid, or we cause a reaction with the acid to remove it.

For more about improving pH (in addition to this method), read "The Secret to Reef Tank pH".

This method of stabilizing pH will use kalkwasser to react with the CO2 in the water in order to maintain a stable pH. Now keep in mind, Chris, and most every hobbyist, believe in stable alkalinity as well. So you need to make sure to maintain both as stable as possible!

Chris Meckley - Discussing the use of Kalkwasser in Elevating pH Levels

By using kalkwasser instead of using a combination of alkalinity and calcium buffers, you can remove a reasonable amount of carbonic acid, which boosts your pH, and rises alkalinity at the same time! While kalkwasser may not supply all of the alkalinity your reef tank demands, by increasing your pH, it decreases the amount of alkalinity buffering needed to maintain stability!

Chase pH, Not Alkalinity - Chris Meckley ACI Aquaculture, Rappin' With ReefBum Sound Bite

Chris notes (in the video above) that when you start dosing kalkwasser, you may notice a spike in alkalinity. In fact, he noted as high as 13 dKh being noticed when switching to kalkwasser. If the coral is not stressed from this alkalinity, do not do anything, and simply allow the coral to uptake the calcium and carbonate until the alkalinity declines. Then you can use a calcium reactor or high quality alkalinity buffer to stabilize the alkalinity levels.

A bit of Science

Initial Boost of Alkalinity (And Why Kalkwasser Stabilizes Alkalinity)

This initial boost in alkalinity is because when Calcium Hydroxide (Kalkwasser) mixes with the Carbonic Acid in the water, it produces calcium carbonate and water (and a spare hydrogen ion).

Ca(OH)2 + H2CO3 => CaCO3 + 2 H2O + H

When the calcium carbonate reacts with CO2 and water, it produces calcium bicarbonate. This calcium bicarbonate is then used to help coral grow their skeleton. Additionally, the Calcium Hydroxide can directly interact with CO2 to produce calcium bicarbonate.

CaCO3 + CO2 + H2O => Ca(HCO3)2

Ca(OH)2 + 2CO2 => Ca(HCO3)2

As you can see, there is an addition of carbonate and bicarbonate. Both carbonate and bicarbonate are "Alkalinity". In reef tanks, we measure Carbonate Alkalinity, which is the measure of how many carbonate and bicarbonate anions in the water.

Read more about this from CorrosionPedia - Carbonate Alkalinity.

Meaning this initial boost of alkalinity is likely due to the removal of the excess carbonic acid and CO2 that have built up in the tank over time. This then stabilizes as the kalkwasser becomes standard/stable in the aquarium.

How does Kalwasser Improve pH

As you can see, the addition of Calcium Hydroxide (Kalkwasser) will remove both carbonic acid and CO2 from the water when producing carbonate and bicarbonate ions. This removal of carbonic acid, as well as the CO2 that will convert into carbonic acid, directly increase pH. (Higher pH means less acid in the solution)

Correlation between Alkalinity and pH

Pulling information from this article by Randy Holmes-Farley, it appears that pH and alkalinity should correlate directly and simply shift based on how much CO2 is present. This means that if you are able to maintain a stable pH, it will cause alkalinity to change as the CO2 levels change. Very much like how we currently look at pH swings in terms of CO2 in the space, alkalinity could be looked at the same way.

Theoretical Relationship between Carbonate Alkalinity and pH

The theoretical relationship between carbonate alkalinity and pH for seawater in equilibrium for preindustrial air

The theoretical relationship between carbonate alkalinity and pH for seawater in equilibrium for preindustrial air (green; 278 ppm carbon dioxide), current air (blue; 350 ppm carbon dioxide) and possible future air (red; 700 ppm carbon dioxide).

(Source: article by Randy Holmes-Farley)

For open-air facilities such as ACI Aquaculture, maintaining a reasonably constant CO2 value is not difficult, but still not perfect.

In a home aquarium, the CO2 levels are going to change somewhat frequently. If the windows are open, you may notice that your alkalinity is at a reasonable level and the pH is between 8.3 and 8.4. Then when the windows are closed for a couple of days, or there are people in the room with the tank, that things are out of whack.

In those cases, I've found that maintaining the same 8.3 pH requires an alkalinity of about 0.5 to 1.0 dKh higher than with windows open. This seems to match the information provided by Randy Holmes-Farley. With an increase of CO2, the alkalinity must increase to keep that direct relationship with pH.

Stable pH vs Stable Alkalinity?

This seems to bring up the same question every time, should we focus on alkalinity or pH then? The answer is, why not both? For years, we have been trying to keep a certain alkalinity and increase pH. The method of doing that has been trying to minimize CO2 from the surrounding space.

With using kalkwasser to stabilize pH, were doing the EXACT SAME THING, we are simply removing the CO2 after it enters the aquarium. The difference is that when the CO2 levels in our homes is higher, we have to raise the alkalinity to allow the pH to stay at those levels. So you may see different levels based on the conditions surrounding the reef tank!

All this being said, in a Thread on Reef2Reef, Randy Holmes-Farley may have said it best...

Randy Holmes-Farley Quote from Reef 2 Reef - Alkalinity Stability or pH Stability

Stabilizing pH with Kalkwasser - ACI Aquaculture Method

The method used by Chris Meckley at ACI Aquaculture is to maintain a stable pH level by dosing kalkwasser when the pH is less than 8.29, ignoring the alkalinity level at first, as it will rise from the release of alkalinity (buffer) being bound by the carbonic acid.

This would make sense as an increase of pH would require a larger alkalinity. And with a lot of CO2 (or carbonic acid) in the reef tank, these levels will likely be higher depending on the amount of CO2 in your reef tank. For my aquarium, I saw the alkalinity go up from 8.5 to roughly 9.5 in this initial process. When the windows are closed for multiple days however, I may have to supplement the alkalinity in order to make up that difference required due to the extra CO2.

How to Stabilize pH in Your Reef Tank

What you need

First off, you will need to use a Reef Tank Controller such as the Neptune Apex. You will also need a dosing pump that connects to your Reef Controller, and a pH probe for the controller at a minimum. Additionally, you will need a LARGE, food safe container such as a Brute trash can for storing mixed kalkwasser.

Chris strongly encourages that you use a piece of foam that has PVC "feet" and it will hold the intake tube for the kalkwasser dosing on the bottom side. This sits in the kalkwasser mix to prevent the skin on top of the solution as well as the unmixed kalkwasser powder on the bottom from being pulled into the tank. (See more about this in the video above.)

Determine Average pH

You will need to use the output of a pH monitor to find the average pH of your tank over a couple of days. For example, my tank pH was between 8.0 and 8.2 for the day. So my average was 8.1. This will change from day to day using this method. Hopefully rising. You will need to adjust your kalkwasser dosing amount for a while as your pH settles in.

Determine Kalkwasser Needs

You will need to know how much water your tank evaporates in a day. For this example, let's assume your tank evaporates 1 gallon per day, or 3785 mL. You will need to mix up enough Kalkwasser to support a full week times 2. In this case, that would be 14 gallons. You will keep that in a Food Grade Brute container or some other food grade container.

Dosing Kalkwasser

Now, you will set a dosing pump (in this case the Neptune DOS), to add double the amount your tank needs to top off over a FULL 24 Hours. For this example, the top-off about was 3785 mL, so you will set the DOS to add 7570 mL from 00:00 to 23:59.

This is because the kalkwasser dosing method will not actually consume the full amount. It will only be on for about half of the time. The reason to do so this way, instead of setting the DOS for only half of the day, is that the tank will automatically determine the time it needs the pH boost and turn off outside of that. So don't worry about it seeming like a lot, but make sure that your tank won't overflow if there is a problem.

Make sure to also keep a standard ATO running in case the method uses less water than planned. This will ensure a stable salinity level as well as water levels.

Connecting Kalkwasser Dosing to pH Level

This is where the magic happens. In your Reef Controller, you will add a control statement to TURN OFF your dosing pump if the pH is greater than your average pH. For the Neptune Apex, this would mean adding the following line to the end of the advanced control.

If pH > 8.10 Then OFF

Adjust And Repeat

As you do this, you should see the average pH change every day. What you'll want to do is modify the line above until you are trying to maintain a desired pH of about 8.25 to 8.30. Chris Meckley targets 8.29. This is because there is no real benefit to maintaining a pH above 8.30 for your reef, but maintaining stability has a GREAT benefit!

Additional Information about Dosing Kalkwasser the ACI Way

Risks and Rewards

While the reward of a stable pH is obvious, this does come with risks. Your alkalinity may swing more than you would like. This may lead to coral losses depending on the type of coral and how well you are monitoring the tank and parameters. Additionally, it will add more water at night, meaning your salinity will be lower at night and higher during the day. Though this shouldn't be much of an issue, it's worth noting.

So why is it that this method may work well, but may also not work? I think it is easiest to say we don't all fully understand how coral "operate". Do they need stable alkalinity, pH, carbonate, and/or bicarbonate? We don't seem to really have an answer... So I will leave you with another Randy Holmes-Farley quote from a Thread on Reef2Reef.

Randy Holmes-Farley Quote from Reef 2 Reef - Caution as we don't know what coral need

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With Chris Meckley using this method at ACI Aquaculture, though skeptical, I am currently testing this method and having positive results. That being said, I have only been doing so for roughly a couple weeks, so there is plenty of learning yet to do!

If you have a small reef tank, or are simply learning to keep coral, I would not advise getting too fancy. Who is this method for? I would only try this if you are a more experienced or advanced aquarist, that knows how to respond to different reactions. Additionally, if you have a small experimental system or are a coral farm, it may be worth more investigation.

I strongly discourage new or beginner level reef keepers from trying to stabilize pH while maintaining alkalinity as there is a level of difficulty that comes with this, and it is important to know how to handle the changes in your reef.

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About the Author

Reef Stable Founder 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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