Calcium is one of the essential elements in our body. It helps to form our bones and teeth. However, apart from human beings, many other living creatures need calcium too. Corals are no exception to this. They need a steady level of calcium to grow and keep their colors away from fading away.

If the water flow and the light are perfectly set in your reef tank and you are still wondering why the corals are not flourishing as expected, you should better have a look at the calcium level. Many complexities might circle the tank and the aquarium creatures if the calcium level is too low. So, how can you raise calcium in your reef tank?

Using Kalkwasser, adding calcium or carbon di-oxide reactors, balanced 2-part supplements, adding calcium chloride, and treatment with the ‘balling method’ are some of the effective ways to raise calcium in a reef tank.

In this article, I am going to talk about some of the symptoms of low calcium levels along with the ideal calcium level. You will also know the ways to raise calcium in your reef tank in detail. So, what are you waiting for? Get some popcorn and dive in.

Symptoms of Low Calcium in the Reef Tank

As many invertebrates need calcium to thrive, low calcium in the reef tank is a common scenario compared to the high calcium issue.

If there is a low supply of calcium in a tank, the development of shells and exoskeletons of the corals and invertebrates gets hindered. Low calcium level is also responsible for the slow growth of corals.

When it comes to slow-growing species, the low calcium level will shrink them back and cause discoloration.

On top of that, low calcium also brings about low pH, low alkalinity, and a drop in water hardness. If these changes take place rapidly, there is a chance that the aquarium organisms will go under a shock and even get killed.

How Often Should You Measure Calcium?

Measuring Calcium, Magnesium, pH, and Alkalinity after a certain interval is a must for if you aim to get a healthy reef tank. How often one should do it depends on his or her opinion and capability. However, the more often you do it, the better it is to strengthen the protection of your tank from sudden shocks.

However, it does not necessarily mean that you have to measure the calcium and other parameters daily. It is actually neither realistic nor possible by most of the tank owners to test the water daily for all the parameters. First of all, it is costly and secondly, it is time-consuming.

On top of that, nutrients like calcium do not go under change every hour. So, checking the water every day might give you the same results repeatedly.

So, what should you do instead? While it is good to check the alkalinity daily, it is completely fine and logical if you check the calcium level per week. It is because calcium level is steadier and it takes time to spike or drop. So, I would recommend you to check the calcium level in your reef tank once a week.

What is the Ideal Calcium Level for Reef Tank?

It is not a tough question to answer. The ideal calcium level in the reef tank should be ranging from 380 ppm to 450 ppm.

Note that, if the calcium level is too low, there will be a deficiency of enough calcium ions to help the corals grow and maintain healthy shells and exoskeletons.

On the other hand, too much calcium can skyrocket the pH level. This is also dangerous as most marine organisms are not capable enough to cope with the drastic changes in pH levels.

So, to keep the marine creatures safe make sure that you are going to maintain a healthy level of calcium ranging from 380 ppm to 450 ppm in the reef tank.

how to raise calcium in reef tank

6 Ways to Raise the Calcium Level in Reef Tank

Now that you know how badly low calcium levels affect the reef tank, it is time to know how to raise the calcium level if it is low in your tank. There are several methods you can try. I would recommend you to apply one by one so that you can discover what works best for you.

1. Use Kalkwasser or Lime Water

Kalkwasser is the German term to mean lime water. It is a solution of calcium hydroxide dissolved in water. Apart from maintaining the pH level in reef aquariums, it works to supplement calcium level as well.

Adding Kalkwasser or lime water is an effective solution to raise the calcium level. You can use Kalkwasser either in liquid or powdered form.

Kalkwasser has become more popular in the United States since the last decade. Before that European aquarists applied this to raise the calcium level in the water.

However, do not make the mistake of adding Kalkwasser in the main aquarium. The best approach in this respect is to use a sump or external filter if possible.

Another thing you should be careful about adding Kalkwasser is the frequency and amount you are applying. If you add much Kalkwasser too quickly, the result will not be positive at all.

High use of Kalkwasser within a short period raises the pH level drastically that can threaten aquatic lives. So, adding the right amount of Kalkwasser after a certain interval is very crucial.


  • Straightforward and use to use.
  • Contains nothing harmful. It releases only calcium and hydroxide ions into the water.
  • Readily available and budget-friendly.
  • Helps to reduce the phosphate level.
  • Ideal for small to mid-sized aquariums.
  • Ensures optimal calcification by increasing pH level.
  • Available from a variety of brands such as Seachem, Kent, Warner Marine, etc.


  • Inhaling the dust while preparing will cause problems as it is caustic.
  • Contains very high pH.
  • It needs to be prepared just before you apply.

2. Use Balanced Supplements

To solve the problem of alkalinity and calcium in the reef tank, many manufacturers have brought out balanced supplements of calcium and alkalinity. C-Balance, Tropic Marin BioCalcium, Seachem Reef Advantage Calcium are some of them.

Most of these compounds feature either liquid or dry formulations of two-parts. While one part deals with the calcium, the other part works to bring a balance in the alkalinity level.

Though these balanced supplements work to maintain both the alkalinity and the calcium, you can stay relaxed about the fact that there will be no unwanted buildup of the compounds.

The use of balanced supplements is getting more popular because they are easy and safe to use.


  • Once you have achieved your target with alkalinity and calcium in the reef tank, just keep using the two-part formulations equally.
  • You can easily tailor or change the doses as required.
  • If used properly as per the direction of the manufacturer, the likelihood of overdose or shock in the tank creatures is very low. So, you can use it without worrying about safety.
  • Balanced supplements are readily available in any online or offline aquarium store.


  • Using balanced supplements for the long-term is very expensive.
  • You have to measure each of the compounds equally and use them daily. It needs more care and time.
  • If you use these supplements, a common problem you might face in the long term regular use is increased salinity in the water.

3. Add Calcium Chloride

Adding calcium carbonate is one of the earliest ways adopted by the reef hobbyists to boost and maintain a steady level of calcium.

However, though it is simple and easy to use, it is appropriate for small aquariums where calcium demand is not so high.

If your aquarium contains some soft corals and small quantities of coralline algae, adding calcium chloride can raise the calcium level in the water.

However, as there is a chance of depleting the buffering capacity of the aquarium in case you add calcium chloride too quickly, it is best to pair it with buffering compounds.

Let’s now see the advantages of calcium chloride to raise the calcium level in reef tank along with the drawbacks:


  • Widely and readily available
  • Inexpensive
  • Easy dose selection and regulation
  • Perfect for small tanks


  • Incorrect use might bring the “see-saw” effect.
  • Affects alkalinity level.
  • Sodium and Bromide level may rise.

4. Add a Calcium Reactor

Investing in a calcium reactor to maintain or raise the calcium level is also a good idea you can think of. If you can use this properly, you can achieve and maintain the desired calcium level safely within the tank system.

Compared to other means of achieving the targeted amount of calcium, a calcium reactor comes with fewer drawbacks. What you need to do is to make some adjustments in the reactor to suit your plan.

Most of the calcium reactors can produce a calcium solution by dissolving calcareous media in water with low pH.

Carbon dioxide in a calcium reactor helps to achieve that low pH. It is the flow rate and the carbon-di-oxide amount that sets the rate of calcium supplementation.

To ensure proper supply of calcium, make sure that you have set an accurate flow and carbon-di-oxide level manually.

Before you turn your reactor on, you have to check and note the calcium and alkalinity level. Keep this result as the reference point or baseline so that you can trace out the progress of the calcium reactor and how good it is performing to scale up the calcium.

Keep testing the water per week to get an idea if your calcium reactor is really helping to bring a balance in the calcium and alkalinity.

There is no doubt that a calcium reactor is one of the effective ways to achieve the desired calcium level in the reef tank. It has many benefits but not without drawbacks. Let’s have a look at some of the advantages and disadvantages of a calcium reactor in the reef tank system.


  • If you can set and use it properly, a calcium reactor can supply calcium automatically to bring the balance with very little maintenance.
  • It is a great choice for large reef tank owners. It can meet the high calcium demand of those huge reef setups.
  • The long-term maintenance of a calcium reactor is easy and affordable. After you buy and set the unit, what you all need to replace are the calcareous media and carbon-di-oxide.
  • Setting up and maintenance of a carbon reactor is quite simple and straightforward.


  • The initial setup is expensive.
  • You cannot start with just buying a calcium reactor. A proper setup will require you to manage a pH controller, carbon-di-oxide tank, needle valve, and CO2 regulator.

5. Use the Balling Method

The Balling method was developed nearly a decade ago. In this method, you use Magnesium, Calcium, and KH uniformly in the tank.

Raising the level of KH and Magnesium is important along with calcium. If you test the water in your reef tank regularly, you might notice that the level of KH drops before the level of calcium and magnesium drop. That’s why KH requires more regular buffering before you think about calcium and magnesium.

There are three-part dosing programs offered by many manufacturers where KH, calcium, and magnesium are combined either in powdered or in liquid form.

Though you will find it easy to use the liquid, we recommend the powdered form as that gives you a better value when mixed with RO water.

Here’s how to apply the balling method:

  • Test the water first for KH, magnesium, and calcium.
  • Add 5/10 ml of KH, magnesium, and calcium and check the individual parameters with the test kit.
  • Now, compare with the previous data that you have recorded before the application of the supplements.
  • The before and after test result will give you an idea about how much the levels have increased. In this way, you can easily decide how much KH, magnesium, and calcium buffer you need to add in the reef tank per week.

Though you can dose the buffer with hands per day or week, it is not a good idea to do it for the long term. First of all, it is time-consuming. And secondly, there is always a chance of overdose or underdose which can be really harmful to the tank creatures.

To solve the problems of hand-buffering, the best way is to adopt an automatic dosing system. In this type of dosing, you will have 3 to 4 peristaltic pumps for dosing the liquid buffers.

One great advantage of an auto dosing system is that you can set the daily and weekly supply easily. This is more stable and feasible for long-term use.

So, to increase the calcium level in the reef tank, try the balling method.

6. Combined Treatment of Calcium Reactor and Kalkwasser

To raise the calcium level in bigger reef tank systems, combined treatment of calcium reactors and Kalkwasser is getting more popular.

If you use both the Kalkwasser and calcium reactor, it is easier to maintain the calcium and alkalinity level at the same time. This method works best for larger SPS reef tanks.

Things to Remember While Raising Calcium in Reef Tank

  1. If you apply Kalkwasser, the night is the best time to use it. It is because this is the time when the pH level remains minimum.
  2. Do not add too much Kalkwasser at the beginning. Use it gradually and increase the dose slowly after a certain interval.
  3. It is better to add calcium as much as required, but not too much. If you add more calcium than the demands of the tank creatures, you might end up destroying the balance of other chemicals such as pH and alkalinity.
  4. You must test the water thoroughly before using any of the methods to raise calcium in the reef tank. Check the pH level, nitrate level, phosphate level, magnesium level, and alkalinity level to understand the water condition perfectly. This will also help you to decide how much calcium you should aim to add in the tank.
  5. A sudden increase in the calcium can drastically raise the pH level. So, make sure that you raise the calcium level tolerably.
  6. Check the salinity and the water temperature before you apply the calcium supplements.
  7. Do not let the Kalkwasser remain idle after you have prepared it. Use it as soon as you make it ready.
  8. While you make the Kalkwasser solution with the powder, use a mask to make sure that you do not inhale the dust.

Frequently Asked Questions (FAQ)

How Can I Get the Best Result from My Calcium Reactor?

To get the best benefits from the calcium reactor to boost the calcium, you have to consider the aspects mentioned below:

Right Media Selection: Choosing the right media that does not contain phosphate is important. There are many media out there that release phosphate. You should buy and set one of them. Fortunately, phosphate-free media are available in the market now.

Size Does Matter: Make sure that the calcium reactor you are buying can correspond to the size of your reef systems. If your system has more SPS corals and coralline algae, you need a bigger reactor.

Though you might get good service from a small or undersized unit at the beginning, ultimately it will no longer be able to meet the calcium demand. It is because it will fail to produce adequate dissolved calcium for your reef tank.

Maintaining pH Level: The stream that passes through the reactor should have a pH level of about 6.5. Reaching this pH level indicates that the calcareous media will dissolve as expected.

If you find that pH level is higher than desired, add more CO2 or decrease the water flow. Doing the former is better than the next because less water flow means you will have less calcium and carbonates in the tank.

Flow Rate Setting: Depending on the size of your tank, the ideal flow rate through the reactor should be set within 1-2 liters per hour. You can make adjustments in the flow rate if you intend to raise or lower the calcium rate further.

However, keep in mind that in case you increase the flow rate, the CO2 bubble rate will also require to be uplifted.

The deficiency of calcium in the reef tank is more common and that’s why you will need to increase the flow rate very often. It is applicable especially when your reef tank has plenty of SPS corals.

CO2 Level: At the beginning, you can set the carbon-di-oxide at 1-2 bubbles per second. It is a must to monitor the CO2 level closely as often as possible.

Make sure that your tank does not get excess CO2 as it is harmful to the fishes and corals.

To regulate the CO2 intake properly, setting a bubble counter, a needle valve, and a pH controller will be of great help.

Proper Maintenance: If you intend to use a calcium reactor for a long period, you have to make sure that you take care of it properly.

It is a fact that by the passage of time, the flow rate of the reactor decreases due to buildup and low efficiency. To increase the lifetime of the reactor, proper cleaning of the reactor along with the valves and the pipes is important.

You should use mild vinegar to thoroughly clean the reactor and get it rinsed properly. Cleaning it once or twice a year will help you to get the optimum performance out of it.

What is the Best Way to Raise Calcium in My Reef Tank?

The answer to this question depends largely on the size of the reef system you own. Combined treatment of Kalkwasser and calcium reactor is ideal for big tanks with a lot of SPS corals.

On the other hand, if you have small or medium-sized aquariums, using Kalkwasser or calcium chloride can raise the calcium safely.

What Will Happen If I Add Too Much Calcium in the Reef Tank?

Too much calcium can affect the fishes negatively, especially if the change is sudden or abrupt. Though some saltwater fishes can survive out of their comfort zone, sudden changes in the water have more evil consequences.

A drastic change in the water chemistry can kill the fishes. Even if they do not die, the change will stress them out.

Erratic swimming, slow growth, lethargy are some of the symptoms in the fishes that denote that the water balance is not preserved. Check our how you can lower calcium in reef tank.

Final Thoughts

Raising calcium in a reef tank is not very hard if you know how to do it. We hope that you now know how to raise calcium in reef tanks safely without bringing a disaster in other parameters.

When you aim to raise the calcium level, make sure that you raise it keeping a balanced pH, magnesium, and alkalinity level. Have a look at the advantages and disadvantages of the methods we have talked about. This will help you decide the method that best applies to your tank.

We always encourage you to test the water regularly so that you can get an idea about what’s going on there. Any incorrect step or overdose in raising the calcium level can put the whole aquarium and the tank inhabitants in danger.

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