April 26, 2011 at 4:34 pm #23470
Written by David Grim
I have talked many ARC Members through the initial setup and fine tuning of their calcium reactors. I thought I would write this up as a reference for anyone else either wanting or thinking about setting up a calcium reactor, or needing some help fine tuning their in-use reactor. This is written based on my experience. Your experience may differ or not agree with what I write. That is fine. This is not meant as the de facto guide to calcium reactors, just what I have used, understand, and what has worked for me. Hopefully, after reading this article, you will not only understand the “how”, but also the “why” behind the use of a calcium reactor.
The Big Four
In reefkeeping, there are four main chemical parameters we try to maintain within a certain range: calcium, magnesium, alkalinity, and specific gravity. Keeping these levels stable greatly enhances the growing environment for corals in a reef tank and allows us a better chance at a successful experience in our attempts to duplicate Nature’s conditions for our corals.
This article will not deal with specific gravity, as it is a relatively straightforward affair to maintain salinity in a reef tank. We are going to discuss the ways to maintain three of the Big Four chemical parameters in a reef tank.
Why are calcium, alkalinity, and magnesium important?
Without trying to get too technical here, these three parameters are important in reef tanks because they allow many of the normal biological processes of coral growth to occur.
Calcium: calcium is an ion that corals use to lay down their calcium carbonate skeletons. Without it, reefs would not be built, and clams could not grow their shells. Seawater has Ca levels of about 420 ppm (parts per million). We should maintain calcium levels in the 360-450 ppm range. Calcium levels below 360 can limit coral growth.
Alkalinity: alkalinity is primarily composed of carbonates and bicarbonates. Corals take up bicarbonates, and process it into the carbonate part of their calcium carbonate skeleton. Seawater has a KH of 7-8. We try to maintain our KH in the range of 7-11 dKH (2.5-4 meq/L).
Magnesium: magnesium is not used extensively in the skeletal structure of corals, its role is that it allows high levels of calcium and carbonate to be maintained in solution in seawater by preventing extensive deposition of calcium carbonate on equipment and surfaces (abiotic precipitation), and basically keeps it available for use by corals for skeletal building. Seawater has magnesium levels of about 1280, and we try to keep our tank levels at 1250-1350 ppm.
All three of the above chemical components are used up in the normal growth and biological processes of the reef tank and must be replenished as they are depleted by the corals.
How do we maintain Ca, KH, and Mag levels in our reef tanks?
There are three ways most reefers do this: water changes, two part dosing, or calcium reactors. Any of the three methods can be successful.
Water changes: if you do frequent enough water changes, you can replenish CA, KH and Mag levels, but the reality is that many commercial salt mixes are lacking in these elements and only water changes are not sufficient to maintain growth in stony corals.
Two-Part Dosing: This is the external addition of the calcium and alkalinity components in separate liquids. Magnesium must also be added. The separateness of the components allows you to vary the volumes of each of the three components to achieve normal levels. In other words, you get to know how much of each component your tank uses each day and maintain a constant level of calcium, alkalinity and magnesium by adding what is used up each day by the tank. 2-part dosing can be automated through the use of small, programmable peristaltic dosing pumps.
Calcium Reactor: this is a process by which existing calcium carbonate (coral skeleton) media is dissolved in a low pH environment and released into the reef tank. Since the media is coral skeletons already containing the proper ratios of calcium, alkalinity and magnesium, the three components are released in proper ratios for the corals in the reef tank to use.
Components of a Calcium Reactor System
The following equipment makes up a calcium reactor system for a reef tank:
a. The reactor itself-typically an acrylic cylinder filled with coral skeleton media (calcium carbonate), with a pump that constantly recirculates the water inside the reactor through the media. CO2 gas is bubbled into the reactor. The gas readily dissolves in seawater, forming carbonic acid, which slowly dissolves the media at a pH of 7 or lower. Tank water slowly enters and exits the reactor, and the water leaving the reactor is called effluent, and it is rich in calcium, alkalinity, and magnesium from the dissolving reactor media. Effluent flow rate is usually controlled via a micro ball valve or a pinch line on the effluent out line. Most reactors have a bubble counter as part of their design, so the bubble rate (bubbles/minute) can be used as a quantitative measurement of the amount of CO2 gas going into the reactor. Water is fed to the reactor via a small dedicated powerhead or pump, or from a ball valve controlled manifold off the main return pump.
b. A CO2 tank, CO2 tank regulator and solenoid. The tank holds a quantity of CO2 gas. It is hooked up to the regulator, which gives you a tank pressure reading and a pressure reading for the CO2 that is being bubbled into the reactor. The regulator is hooked to a solenoid, which is an electronic valve which is either on or off. When on, it allows CO2 to pass to the reactor, when off, it stops the gas. You typically use airline size tubing to flow CO2 from the tank/regulator assembly to the reactor gas inlet fitting, and there is usually an in-line check valve between the regulator solenoid and the CO2 inlet on the reactor. The check valve prevents water from back siphoning from the reactor to the regulator, which could ruin the regulator assembly.
c. A controller that starts/stops the solenoid based on the pH of the water inside the reactor. The pH of the effluent is measured thru the use of a pH probe, usually placed in the lid of the Calcium Reactor in a probe port, then connected to the controller via a BNC connector. The pH controller/probe must be calibrated to work properly (display the pH inside the Calcium reactor accurately). This means you calibrate the controller/pH probe before you place it in the reactor, and you calibrate the probe regularly, once every 3-4 months I would suggest.
d. Reactor media. This is the calcium carbonate coral skeleton media that is placed inside the calcium reactor. Most manufacturers recommend either large or medium size media.
Reactor System Hookup.
This section is general only. Each reactor, CO2 regulator and Controller is made a bit differently and has its own instructions. There are specific instructions regarding how to turn on the CO2 gas after the regulator is attached to the CO2 tank so you do not damage the regulator. These should be provided with your regulator, and can vary depending on the design of the regulator.
The CO2 regulator/solenoid attaches to the CO2 tank. There is usually a needle valve of the output side of the solenoid. You fine tune/adjust the bubble count with this. The solenoid plugs into the power outlet controlled by the controller. The CO2 line connects to the CO2 IN inlet on the reactor. The water feed line connects to the Water IN inlet on the reactor. The Effluent Out line goes and empties into your sump or tank. Your calcium reactor recirculation pump plugs into an electrical outlet, as does the water feed pump.
Control Parameters of a Calcium Reactor
There are three things you can adjust in operating a calcium reactor, and each will have an impact on the amount of Ca, KH and Mag you are adding to the water, or the rate at which the reactor media is dissolving. And each is adjusted based on the needs of your corals. These control parameters are:
1. CO2 Bubble Rate: How many bubbles per second are going into the Calcium Reactor?
2. Effluent flow rate: How many milliliters/minute are going into/out of the reactor?
3. Controller setpoint pH setting: At what pH inside the Reactor does the controller energize the solenoid on the CO2 regulator and start bubbling CO2 into the reactor?
What happens when you change a Control Parameter:
1. CO2 Bubble Rate
a. increase-more CO2 goes into the reactor, forming more carbonic acid, dissolving more media, resulting in more calcium, alkalinity, and magnesium in the effluent returning to the tank.
b. decrease-less CO2 goes into the reactor, forming less carbonic acid, dissolving less media, resulting in less calcium, alkalinity, and magnesium in the effluent returning to the tank.
2. Effluent Flow Rate
a. increase-there is less contact time in the reactor for the media and the effluent, so less calcium, alkalinity, and magnesium are dissolved in the effluent returning to the tank.
b. decrease-there is more contact time in the reactor for the media and the effluent, so more calcium, alkalinity, and magnesium are dissolved in the effluent returning to the tank.
3. Controller Setpoint pH Setting (example-raising or lowering the pH setpoint from 6.6 to 6.7, or 6.6 to 6.5)
a. raise the setpoint- the controller opens the solenoid valve at a higher pH, resulting in less CO2 going into the reactor, forming less carbonic acid, dissolving less media, resulting in less calcium, alkalinity, and magnesium in the effluent returning to the tank.
b. lower the setpoint-the controller opens the solenoid valve at a lower pH, resulting in more CO2 going into the reactor, forming more carbonic acid, dissolving more media, resulting in more calcium, alkalinity, and magnesium in the effluent returning to the tank.
Setting Up and Tuning a Calcium Reactor My Way.
You should, by now, have your calcium reactor system set up. I would get it running with water going in and out, but no CO2 gas going into it for 24 hours after startup (solenoid unplugged). This will clear all air from the reactor, and allow you to check for any leaks in the reactor plumbing connections.
1. Buy yourself three quality test kits, one for calcium, one for KH, and one for magnesium, either Salifert or Elos. Other brands are available, but these two brands are widely used and respected. I use Salifert and have found it reliable. You will be testing daily upon initial setup and usage of the reactor, and weekly-biweekly after you get your reactor dialed in. I advise recording your test results with the date each time. This helps identify trends in your reef chemistry.
2. Adjust your tank water to your desired parameters with additives. Example: calcium 450, KH 8, and mag 1350. Stay in the recommended ranges. Test and write the Ca, KH and mag levels down next to the date you tested. You need to have these in normal range, then you start your calcium reactor to maintain these levels.
3. Set your controller setpoint pH to 6.6. If your controller has a settable hysteresis (DA or Neptune), set it to .02-.03 units of pH. Independent controllers like the MI SMS 122 have a pre-set hysteresis that cannot be adjusted by the user.
4. Set your bubble count to 60-70 bubbles per minute. Get a watch or a kitchen timer and count how many bubbles pass through the counter in a minute. Adjust with the needle valve on the solenoid as needed.
5. Set your reactor effluent rate at 50-60 ml/minute. Measure the effluent output in a cup for 60 seconds and adjust up/down until you have 50-60 ml in the cup after 1 minute. This rate roughly equals a very fast drip. Almost, but not quite a stream of water. You can open the effluent valve to a stream, then slowly close it until you have just a fast drip.
6. Let the controller run like this at these settings for 24 hours. After 24 hours, test your calcium, alkalinity and magnesium levels again. If they are close to your initial levels, wait another 24 hours and test the next day. If you find your levels dropping or rising, refer to 7 below.
7. What control parameters to adjust:
a. I have found for the past three years that an effluent rate of 50-60 ml/minute and a bubble count of 60-90 bpm (bubbles per minute) is perfectly fine and these two parameters do not need adjusting. If your CO2 Bubble Rate is near 90 bpm, make sure you are not overpowering the reactor’s ability to absorb all the CO2 you are feeding it. You are using too much CO2 if you see gas collecting at the top of the reactor. Adjust it down to the middle or lower end of the bpm range if you see this. Calcium reactor output can change over time due to the effluent out line getting clogged or calcium carbonate or salt collecting inside or at the tip of the effluent out tubing. I have to adjust mine back to a fast drip every few days. Bubble counts stay pretty steady and do not need adjusting after you are dialed in.
b. The easiest way to adjust a calcium reactor for more calcium, alkalinity and magnesium in the effluent is to change the controller setpoint pH setting. I have just found it easier to keep the bubble rate and the effluent rate constant and adjust the controller setpoint up or down as needed. If you need to raise your levels a bit, lower your controller setpoint by .5-.1 units of pH and test for a few days. The lower the setpoint, the more CO2 gas will go in, dissolving more media, and releasing more calcium, alkalinity and magnesium into the tank. If you see your calcium, alkalinity, and magnesium levels rising, raise your pH controller setpoint up a bit until you see consistent test results for a few days. This decreases the amount of CO2 entering the reactor, and lessens the amount of media being dissolved.
c. The end objective is to get several days of constant readings without much drift up or down. When this is achieved, you can readjust the tank water calcium, alkalinity and magnesium levels to what you want with additives, and the reactor should maintain those levels for you. You want the reactor to release calcium, alkalinity, and magnesium at the same rate it is used up in the reef tank.
8. Your calcium reactor is now initially dialed in. Regardless of what method you use, regular testing for Ca, KH and mag is needed, every 1-2 weeks. After you get some experience using the reactor, you may increase this testing interval to your own comfort level.
9. Periodic adjustments of your controller setpoint may be needed as your corals grow. SPS frags use very little ca, mag and alkalinity compared to large colonies. I had to go to a larger calcium reactor (more media capacity) when my acropora colonies started getting big, as my first reactor could not keep up with the demand. Over time you will see the amount of media in the reactor lessen. This will need to be replenished every few months. If you let the media levels in the reactor get too low, you will see the ca, alk and mag levels drop as there is not enough media to maintain them at that bubble, effluent and controller setting. This can be compensated for to a point by lowering the controller setpoint, but if you take a calcium reactor setpoint to a pH of 6.4 or lower, be careful the media does not dissolve on you and turn into mush. Larger grain media can go lower pH than medium grain media.
Here are two articles, one by Marc Levenson and one by Simon Huntington, that talk about setup and fine tuning calcium reactors as well. Marc’s article has most of the parts and hookup of a Calcium Reactor system pictured and labeled, and Simon’s article deals a bit more with the chemistry side of it. Their advice regarding bubble and effluent rates differ from mine, but this shows there is more than one way to successfully set up and dial in a calcium reactor.
Thank you for reading this, and please PM me if you have any specific questions.
Initial pH controller Setpoints for Specific Type Reef Tanks, or at what pH does the CO2 Flow? (Thanks Hnguyen for the suggestion)
Different type reef tanks have different calcium, magnesium, and alkalinity demands, usually tied to how many of your corals lay down a calcium carbonate skeleton as they grow. The more corals that do this, the greater the demand. If your reef tank is mostly soft corals and zoas, for example, you probably do not need a calcium reactor, and could provide the needed elements through water changes or light 2 part dosing. It might not be worth the cost of setting one up for a soft coral tank, but that is up to the reefer to decide.
The following controller settings are suggested with the effluent rate set at 50-60 ml/minute and a CO2 bubble rate of 60-90 bubbles per minute. These initial setting are on the higher end so you do not run the chance of spiking your KH while dialing in your reactor.
Mixed Reef Tanks (soft corals, LPS, maybe a couple SPS): Start with a pH controller setting of 7.3 or 7.4 and test your ca, mag and KH daily. Adjust down in .1 pH increments if your levels test low or start to drop. Raise up in .1 pH increments if they increase. Your goal is steady readings where you are adding the same amounts of ca, mag and kh as it is used up in the tank. My 100 gallon mixed reef tank has a GEO 612 reactor with a MI SMS122 controller, and my controller setpoint is 7.1 and has been for months.
Mixed reefs with more SPS/LPS than soft corals: Start out at 7.0 and follow the Mixed reef instructions for raising or lowering the controller setpoint.
SPS dominant Tanks: Start out at a controller setting of 6.8 and follow the Mixed reef instructions for raising or lowering the controller setpoint. My GEO 818 calcium reactor on my 300 gallon SPS tank has a controller setpoint of pH 6.5 with a hysteresis of .03.
*The thing to be very aware of here is that making adjustments to a calcium reactor is like trying to stop an ocean liner: you make the adjustments and then wait to see what happens. That is why we test for 2-3 days after we make adjustments, to see if they are good or if the controller setpoint needs further adjustment. Alkalinity (KH) tends to respond the quickest when we change controller setpoints, but if you are in proper range regarding KH, I would not worry about fluctuations of 1 dKH or so. If you lower the setpoint, you should expect a rise in KH, and if you raise the setpoint, you should expect a drop in KH.
Smaller Volume Reef Systems and Do I even need a Calcium Reactor?
This Section is based on a PM I received from an ARC Member with a RSM 250 tank.
I always turn to you for sound advice. I am looking into a calcium reactor for my tank. I have heard that they make a world of difference to keep things stable but I have also heard that if I don’t have major swings in Alkalinity and pH that it is a waste of money. It isn’t the cheapest thing, but I am wondering if it is a worthwhile option. Obviously it wouldn’t hurt to have one but is it worth the money?
Your tank being about 65 gallons, you are on the cusp of maybe not needing one. I would go about it this way, do you need one? How have your KH/Ca/Mag levels been over the past couple months? Are your water changes maintaining your levels? If it is not broken, then maybe don’t fix it. Your corals may not be at the point of needing that level of Ca/KH/Mag supplementation.
A calcium reactor is good, but with a smaller volume system it is a lot easier to overdose the tank with a calcium reactor if you are not testing and dialing it in as you should. It is a lot easier to OD anything in a smaller volume of water for that matter.
Reactor dial-in requires a lot of testing initially to get it right, so if you are not willing/able to do this then I would not recommend a reactor for you or anyone.
There is also the cost vs benefit point of view. There is a certain minimum price of admission to a calcium reactor setup no matter what size one you buy. pH controllers, regulators and CO2 tanks all cost the same no matter the reactor size. Main cost variance is the size of the reactor, generally the bigger the reactor is, the more expensive it is.
You can buy a lot of salt or 2 part solution for the initial cost of a reactor setup, so it is just another thing to think about. I did some rough calculations and it was at about the 1.5 year mark where you actually started saving money with calcium reactor up front costs vs 2-part dosing ongoing costs for the 300 gallon net system I had at the time.
That being said, if you decide you must have a reactor, and I understand this because I am a reef gadget freak to the max, you need to decide what brand/size (system volume capacity) you need.
Two things to consider:
1. The rated capacity of the particular reactor.
2. Are you going to go to a larger system in the future?
If you are near the upper limit of a reactor’s volume rating, then go to the next one. Likewise, if you think you are going to upgrade to a larger reef tank in the future, you may consider upsizing your model now to avoid double buying Reactors when you do.
My experience with particular Reactor Brands is limited to MRC and GEO Calcium Reactors. Both are well made and work well, IME. And both manufacturers have very good Customer Service. MRC is an ARC Sponsor. Both of these manufacturers have very realistic system volume ratings on their various calcium reactor models.
Another thing to consider are your space limitations. Some reactors can be run externally or in-sump, whereas others cannot. So if you like a GEO reactor, but it only comes with a Pan World circulation pump, you are limited to external installation, whereas, if an MRC reactor comes with a Mag or Eheim pump, then it can be an external or an in-sump application. Another thing to be aware of as you make your buying decision.
Calcium Reactor is dialed in, but mag levels are still low.
Let’s say your reactor is dialed in and maintaining KH and Calcium levels, but you still find your magnesium levels too low. The following are some possible explanations, and each could be the reason, or could be partially the reason. And if anyone has other explanations, please post in the thread about them.
1. The reef is using more magnesium than the reactor can provide, meaning non-coral animals that lay down calcium carbonate shells, soft corals, and any other chemical reactions are using magnesium at a rate greater than a calcium reactor alone can provide. This was brought up by jmaneyapanda.
2. The salt mix you are using is deficient in magnesium to start with, so the additional magnesium you supplement is basically playing catch up with a deficient amount in the salt mix you buy. I doubt anyone would dispute that this could be the reason as well. I pointed out the AWT Salt Water mix study that showed of 13 major brands of synthetic sea salt tested, 70% were deficient in magnesium levels out of the package.
3. You are using Kalkwasser in addition to a Calcium Reactor, which can affect where your reactor is dialed in and can lead to magnesium being delivered in insufficient amounts to the water column. I reference another article in the Randy Holmes Farley Reef Alchemy series, which is very informative for those doing, or considering dosing kalkwasser, and helps in understanding what I am posting below.
Follow me on this as I try to explain: The basic premise of Calcium Reactor operation is to maintain proper Calcium, alkalinity and magnesium levels in a reef tank. Since reactor media is coral skeletons, dissolving it should release calcium, bicarbonates, and magnesium in the ratios in which they were incorporated by the corals as they lay down their calcium carbonate skeletons. Kalkwasser adds calcium and hydroxide. The hydroxide ion combines with CO2 and turns into bicarbonate, so kalkwasser adds calcium (directly) and bicarbonate (indirectly), so dosing kalk provides calcium and KH to the tank, but not magnesium.
So if you are dosing kalkwasser in addition to using a calcium reactor, your reactor is going to be dialed in at a level that also reflects the calcium and the bicarbonates being added by the kalkwasser, but not the magnesium. You are getting a percentage of total calcium and bicarbonates from the calcium reactor and the kalkwasser, but magnesium is only coming from the calcium reactor, so the reactor settings will be dialed in to maintain Ca and KH levels steady, but you will be deficient in magnesium over time since none is coming from the kalkwasser.
As a result of using a calcium reactor and kalkwasser, you should see slowly decreasing magnesium levels over time, requiring external magnesium supplementation over and above what a calcium reactor setup could provide alone.April 26, 2011 at 4:34 pm #329257
Nice write up.April 26, 2011 at 4:34 pm #329264
Great write up Dave. I learned a lot from reading that. You should “sticky” that somewhere.April 26, 2011 at 4:34 pm #329266
Great write up Dave. There’s a lot of people putting off connecting their calcium reactors right now due to the fact that they lack the info. This will help out many people down the road! I wish I had this when I was setting mines up. I just closed my eyes and did it hoping nothing will die! :whistling:April 26, 2011 at 4:34 pm #329267April 26, 2011 at 4:34 pm #329268
Good job Dave this place wouldn’t be the same without you Bud!!!
+1 to sticky I dont have one yet or need one really but If I do I will review this again.
Thanks again bud for taking the time to write this up!!April 26, 2011 at 4:34 pm #329270
Thanks Dave, I was wondering how fast the effluent should be tuned back to, so that answered my question.April 26, 2011 at 4:34 pm #329357
Excellent information Dave! Purchasing a used Cal Reactor this weekend and this will help me along the way!April 26, 2011 at 4:34 pm #329361April 26, 2011 at 4:34 pm #329410
Thanks for all the kind words. If anyone reading this thread has specific questions, post them and we can get them answered.
I plan on adding a couple supplements to this primer, like proper reactor sizing for system volume, or anything else that relates. If anyone would like a particular area relating to calcium reactors addressed calcium that is not covered in the Primer, post here as well and I will try to address it.April 26, 2011 at 4:34 pm #329430
Thanks Dave. I have a question. I have a dual chamber MRC, which is overkill for my current system. I have around 100 gallons total water. Should I still fill both chambers with media and just do a slow effluent drip, keep the co2 bubble count low, or just fill one chamber? Any help would be appreciate.April 26, 2011 at 4:34 pm #329446
Perfect timing Dave as I am just setting up your old GEO 618.
Thanks!April 26, 2011 at 4:34 pm #329450
Corigan;640043 wrote: Thanks Dave. I have a question. I have a dual chamber MRC, which is overkill for my current system. I have around 100 gallons total water. Should I still fill both chambers with media and just do a slow effluent drip, keep the co2 bubble count low, or just fill one chamber? Any help would be appreciate.
A dual chamber MRC is definitely big, but you can use it for your system. The second chamber is to raise the pH of the low pH effluent coming from the chamber that has the recirculating pump on it. If you are using a controller you can just raise the setpoint to a high enough level where the KH, Ca and Mag levels are where you want them. for example, I have a GEO 612 on my 100 gallon reef (smaller than yours, and 1 chamber). The controller is set at 7.1 pH. You can also slow the effluent or lower the bubble count, whatever you are comfortable with. Refer to the Changing a Control Parameter section of the Primer. You should be fine at 50 ml/min effluent and a CO2 bubble rate of 60 (low ends of the two parameters, and just raise the controller setpoint to where the reactor maintains the levels you want.April 26, 2011 at 4:34 pm #329452
Awesome, thanks Dave. I am going to be leak testing and getting my co2 bottle refilled this weekend and will post updates as I work on getting this reactor setup.April 26, 2011 at 4:34 pm #330987
Dave, If I may make a suggestion. This is about what I PM’ed you for with my set-point for my controller. If you can make a guideline as to where one should set their controller to turn on and off the co2 at. I know this will very with everyones tank, but maybe a general guideline for a heavy SPS tank and one for mild SPS. Something like that?
I think that will help answer a lot more questions about setting up a reactor as well. That why you won’t get people like me PM’ing you about it!! 😀
HoangApril 26, 2011 at 4:34 pm #330989April 26, 2011 at 4:34 pm #330993
Hnguyen;643824 wrote: Dave, If I may make a suggestion. This is about what I PM’ed you for with my set-point for my controller. If you can make a guideline as to where one should set their controller to turn on and off the co2 at. I know this will very with everyones tank, but maybe a general guideline for a heavy SPS tank and one for mild SPS. Something like that?
I think that will help answer a lot more questions about setting up a reactor as well. That why you won’t get people like me PM’ing you about it!! 😀
Great idea Hoang. I will add this to the Primer. But I don’t mind the PM questions either!:DApril 26, 2011 at 4:34 pm #330995
Acroholic;643834 wrote: Great idea Hoang. I will add this to the Primer. But I don’t mind the PM questions either!:D
Cool beans Dave! You da man!! :thumbs:April 26, 2011 at 4:34 pm #331001
Initial controller setpoint section added to Primer.April 26, 2011 at 4:34 pm #331004
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