Both low and high calcium levels in your reef tank can impact the health of the living things in your tank. If the calcium level is between 380 to 450 ppm, you don’t need to worry. But if the calcium level exceeds 450, you need to take necessary steps as soon as possible.

Two of the most convenient ways to lower calcium in a reef tank are to either wait for the calcium to get low automatically, or if you want a fast solution then stop using various calcium supplements. You can change the whole water of the tank as well.

Easier said than done, but don’t worry. I won’t leave you just by telling the solution, to know in detail about what are the things you need to do to lower calcium in your reef tank, stay tuned.

How to lower calcium in your reef tank: 3 Simple Techniques

There are many ways of lowering calcium you will find on the internet. Even reading them will be a waste of time for you, let alone applying. Just so you don’t have to go through the trouble of finding the best solution, I have gathered a few solutions which work the best and are popular among reef tank or aquarium owners.

How To Lower Calcium In Reef Tank

You should go for one option at a time, and figure out which one works best for you. Remember high calcium in your reef tank is not that of a big issue, the solutions are simple and less time consuming.

1. Wait till calcium levels get lowered

As you notice the calcium level is a bit higher, you don’t need to panic. Simply wait for a week and you will see it decreasing. As long as the calcium level is not exceeding 550 ppm, it’s not a crime if you wait.

Keep on observing for a few weeks. There can be any reason behind the fluctuation of calcium level in your reef tank, so without being sure about it you should not take any step. As long as you don’t see any sudden change in calcium level, you still should wait.

And if the level of calcium is not skyrocketing even after a few weeks, it’s expected that now the level will decrease automatically. And as it’s dropping your problem is being solved as well. Just by being patient, you can deal with high calcium levels if you are lucky.

2. Stop the supply of calcium

If waiting has brought no result for you, first of all, my sincere apologies. Let’s look at what you should do now to lower the calcium in your reef tank. You might find the solution a bit strange, but lots and lots of people loved the solution.


Let’s jog your memories first and remember whether you have used alkaline and calcium supplements equally at the beginning when the water was stable and fresh. Now after a few months, we are looking at high calcium levels which can be lessened by simply skipping a few days of dosing calcium in your reef tank.

While applying doses to water, skip the calcium and just add the alkaline part. As a result, there will be no more new calcium and the corals living in the water will absorb the excess amount of calcium. And within a few days, the calcium level will drop back to normal.

Another reason why this method is so effective is because this increases the alkalinity in water. The increase in alkaline helps to decrease calcium as well. Now that you understand the process, you might be wondering for how long you should skip on adding calcium?

The answer is as simple- keep on skipping until the level drops down to the safe calcium level. Which is from around 380 to 450 ppm.

3. Changing the reef tank water

If waiting or skipping calcium dosing didn’t work, maybe your reef tank already is highly overdosed. At this stage, your solution is to change the water completely and add new water. It’s usually the last option when all the other options fail.

Changing whole water is a bit costly process, especially if you have a large reef tank. To lower the cost you can change 15 to 25 percent water every week. And while adding new water it’s better if you add a lower or normal ppm ranked salt mix.

Depending on your luck, you might start seeing results after a few weeks of replacing water. Usually, people get the best result after around a month or so. While changing the water, don’t forget to maintain other elements in the water at a sustainable level for the fish. Especially monitor the phosphate level and make sure it’s well under the parameter.

How can you test the calcium in your reef tank?

Checking calcium levels in water from time to time is a must. You should check alkalinity as well while checking the calcium levels and make sure you check at least two to three times a week. But how are you going to check?

You can buy any reliable kit from any home depot store. Make sure you buy a kit made by a well-known brand. By using the kit, you will know the calcium level within minutes without any hassle. “Hanna” and “Seachem” are two of the best calcium level test kits out there. You can easily get them from amazon.

Read Next: Saltwater/Reef Tank Parameters

What happens when you have excessive calcium in your reef tank

Calcium carbonate forms when you have too much calcium in your reef tank. High calcium in water often causes damage to your heaters and the pumps as well.

If the calcium level in your tank water surpluses 500 ppm, the level of alkaline will surely drop. Calcium and alkaline are inversely proportional. The adequate level of alkaline should be at least 7 dKH, and the maximum can be 11dKH.

When the alkalinity decreases as a result of the increase in calcium, the overall buffering capacity of your reef tank water is hampered. And when buffering does not take place as it’s supposed to, the ph level starts to fluctuate. Which is not an ideal condition for the corals you have in your reef tank.

On the other hand, excessive calcium in water influences other properties in water as well and creates an imbalance among them, altogether making the water condition unsustainable for aquatic lives. High calcium causes stress to the fishes and invertebrates.

If you see any symptoms like slow growth, lethargy, erratic behavior, coming near the surface, etc. it’s an indication that your reef tank water is probably overdosed with calcium.

Why do you need calcium in your reef tank?

If you are wondering why you even need calcium in the first place, this part is for you. The kinds of fishes living in your tank, especially if they are corals, they need calcium supply in order to grow and get bigger efficiently.

The corals living in your reef tank absorb calcium continuously from the tank water. So maintaining an adequate supply of calcium is needed. Depending on how many corals you are growing in your tank, you need to supply calcium. But you need to be mindful about not overdosing.

There’s a limited parameter on how much calcium you should use on how many gallons of water. Also depending on how many fishes. Keeping the balance of fish and water volume, you need to supply calcium. Without a proper balance, the water chemistry will be ruined and harm the fishes.

Frequently asked questions

Will high calcium kill corals?

Yes, super high levels of calcium in your water might cause death to corals, so always be careful to keep it under 500 ppm.

What is the safe Reef tank calcium level?

You should try to maintain the level of 380-450 ppm to be on the safer side.

What is the relationship between calcium and alkalinity levels?

They are inversely proportional ,which means if one increases the other one will decrease.


I hope this article makes you understand that excessive amounts of calcium in your reef tank is not something to freak out about. Rather what you can do is follow the solutions I have provided and teach others as well about how to lower calcium in reef tanks.

Make sure you are always careful so the levels of various components stay under their respective parameters.

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