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Control pH and Alkalinity at the Same Time

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Last updated on March 3rd, 2024


How to Start Dosing Calcium, Alkalinity and Magnesium in Reef Tanks

Fully Control pH and Alkalinity

This article is going to combine a couple of other articles and topics. This is an advanced guide for maintaining a stable pH and alkalinity. I'll talk about the method I am planning to use. Being able to dose for pH and alkalinity will give your reef the best environment for coral growth!

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Please remember, this is an advanced topic, and is not required for a successful reef. If you're ready for this type of control, make sure to do so at your own risk.

What Do You Need To Control pH and Alkalinity

Okay, I'm going to be direct. Dosing for both pH and Alkalinity is not going to be cheap. That's why typically only coral farms and large tanks consider it. To start, here is what you'll need:

  • Neputue Apex
  • 2x PM1 Modules
  • 3x pH Probes
  • Neptune Trident
  • Neptune DOS
  • Calcium Reactor
  • Kalkwasser Mixing Container (Brute Trash Can)

Substitutes and Reminders

First, it doesn't have to be a Neptune Apex. Any controller that can manage outlets and can support 3 pH probes, measure alkalinity, and a doser will work!

Additionally, if you would prefer to use a kalkwasser reactor, and it works for the amount of kalkwasser you need, that is plenty sufficient.

Finally, remember that for the calcium reactor, you will need things like the solenoid, feed pump, CO2 tank, etc. I am assuming you know how to set-up and manage a Calcium Reactor in this article.

Before We Start

We will need to decide on a few target values before we start. We need to know what pH and alkalinity you're trying to achieve. You also need to know an emergency shut off number for alkalinity. If the alkalinity goes above that number, you shut the whole system down so you don't kill your reef. Here is what I use:

  • Target pH: 8.3
  • Target Alkalinity: 10.0 dKH
  • Emergency Shutoff Alkalinity: 11.0 dKH

Step 1 - Controlling pH and Alkalinity Using Kalkwasser

This part will be a quick rehash of ACI Aquaculture's pH Control with Kalkwasser Dosing.

Start by setting up a large kalkwasser mixing container such as a Brute Trash Can or a Kalk Stirrer. If you have a larger amount of water, over about 200 gallons, you may see too much water needs to be dosed through the kalk stirrer and it may not be able to keep up. In that case, you'll want to pre-mix the kalkwaser and store it in the brute trash can.

Then you will want to set up 2 pH probes in your sump/reef tank. Why 2 pH probes? Because if 1 fails, you'll dose 35 gallons of kalkwasser to your reef. Don't ask me how I know...

Now that we have all of that set up, what you will do is set your kalkwaser doser to add roughly double your total daily top off. Have this set to dose across the full day. Keep in mind, this should not really going to dose that much. The idea is that it may add your full top-off at night, then nothing during the day. So it should all even out. But the rest is just in case your reef gets a little off the pH needed during the day.

Now, you're going to want to add the following advanced control (This is for the Apex) to lock in the pH. You'll need to tweak the probe/alk names to whatever they are on your Apex and the numbers to match your target pH and emergency alkalinity.

      If pH > 8.30 Then OFF
      If pH_2 > 8.30 Then OFF
      If Alkx7 > 11.00 Then OFF

This will dose the amount of kalkwasser you set up until the pH reaches 8.3. It will also turn off the dosing if the alkalinity hits 11 dKH as an emergency shut off.

It's best to do this during a season where you can keep your windows open to raise pH that way. While your reef get's buffered and to the desired pH, it can use more kalkwasser to hit the desired number. That's where the fresh air will help to reach it on less kalkwasser.

Step 2 - Controlling Alkalinity Using a Calcium Reactor

The Calcium Reactor is one that you will need to set up the way that best fits your needs. I encourage a continuous dosing pump like a Kamoer Dosing Pump. This will help you dial in the amount of alkalinity that you dose. Additionally, I don't do as much with counting bubbles. I have a higher CO2 flow to bring the reactor pH down to about 6.45 quickly. Then I have the solenoid maintain this when I need the reactor to run. But I keep the feed and recirculating pumps running at all times.

This way, it adds alkalinity as needed, but not constantly. Saving a lot of complexity. Here is the code I use in the Neptune Apex to control my CO2 solenoid:

      Fallback OFF
      Set OFF
      If CaReac > 6.50 Then ON
      If CaReac < 6.45 Then OFF
      If Alkx7 > 10.00 Then OFF
      Defer 000:30 Then OFF
      Defer 003:00 Then ON

This should keep the pH in the reactor roughly between 6.45 and 6.5. Additionally it will turn off if the alkalinity is above your target alkalinity. The defers just help make sure that the solenoid isn't constantly turning on and off to keep the equipment safe.

So, the next question is why does it have to be a calcium reactor and not 2-Part? This is actually fairly easy to answer. You can use 2-part, but it won't work as well. The calcium reactor lowers the tank pH because the water in the reactor is about 6.5 pH. 2-Part will raise the pH. Which will make it harder for the kalkwasser to do the control.

Things You May Notice

You will notice that with the windows open, and higher pH in the tank, that the kalkwasser will run less and that the calcium reactor will run more to maintain alkalinity. The kalkwasser will only run to keep the pH correct if the calcium reactor drops the pH too much.

There is likely going to be a point where the calcium reactor lowers pH and kalkwasser kicks in but then there is double duty on alkalinity dosing. This is why the Trident's 4 measurements is important. This should help shut everything down if alk gets too high. But remember, this is a risk that you'll need to watch for if you do this method of maintaining alkalinity and pH.

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This is the simple, yet advanced way that I maintain a stable pH and Alkalinity using kalkwasser and a Calcium Reactor. While there are other methods such as using 2-Part instead of a calcium reactor, it just isn't as effective. Remember that this is a fairly advanced method of dosing, and is really only recommended if you have a large tank where kalkwasser or another method alone isn't able to maintain your reef the way you'd like. Even at that, remember, this is risky and confusing. So set this up at your own risk!

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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!

About Reef Stable

Reef Stable was initially founded in 2019 as a reef tank parameter log to fill a need. Reef Stable quickly grew, becoming a location to solve all of your reef tank problems as well as a place to learn.

Reef Stable now provides a Reef Blog, Reef Aquarium Guides, Coral Care Guides, Identification and Solutions for Pests and Algae, and Reef Dosing Calculators, in addition to the original Reef Parameter Log.

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