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How To Add Calcium To Freshwater Aquarium? 12 Proven Ways!

How To Add Calcium To Freshwater Aquarium? 12 Proven Ways!

Calcium is indispensable for saltwater aquariums. Therefore, utmost attention is given to maintaining the optimum calcium level for marine creatures. However, we seldom hear or read about its importance in freshwater aquariums. 

Do freshwater creatures require calcium? What are the consequences of calcium deficiency? And how to add calcium to a freshwater aquarium?

The answers are “yes,” “grim,” and “we’ll discuss it below,” respectively. 

So, yes – calcium is vital for all freshwater species in varying degrees. And there are one too many ways of adding calcium to freshwater aquariums. 

We’ll discuss everything there’s to know about it. 

A Brief Intro On Calcium Concentration In Water Bodies 

Natural water bodies like rivers, lakes, and springs have calcium deposits due to the erosion of the stones. And naturally, nearby fish, plants, and inverts absorb the calcium from the water to boost their growth and wellbeing. 

Depending on the landscape, the calcium concentration in these waters can range between 0.5 milligrams per liter and 75 milligrams per liter. 

For example, the lakes in the American Midwest have a calcium concentration of around 20mg per liter. That’s about 0.003 oz per gallon. On the other hand, marl lakes in areas with high limestone deposits have much higher calcium levels. 

The lowest calcium concentrations are found in the boreal zones of Europe and Canada, where the calcium levels clock in around 5mh per liter. That’s about 0.0007 oz per gallon. 

Why Do Freshwater Fish Need Calcium?

Freshwater fish need calcium to grow, build skeletons, and make eggs. Therefore, calcium additives are essential for a freshwater tank as it has less natural water hardness than a saltwater tank. 

By the way, water hardness refers to the amount of calcium and magnesium dissolved in the water. And it’s pretty important to get this parameter right. 

Freshwater fish absorb required calcium from their diet and are less dependent on their environment for dissolved calcium. But still, it’s vital to maintain the right hardness level on par with their natural habitat. 

Why Do Shrimps, Crabs, And Crayfish Need Calcium?

Shrimps, crabs, and crayfish have exoskeletons (external skeletons) that limit the extent of their growth. Therefore, the only way they can grow is by molting.

So, molting is the process of shedding the old exoskeleton and building a new one. And they need plenty of minerals like calcium to create a new exoskeleton. 

For instance, a study has shown that 30-50% of a shrimp’s shell is pure calcium carbonate. That’s quite a lot!

Like fish, these inverts can absorb calcium from water and diet. 

If there’s a calcium deficiency, they will have difficulty molting and building a new exoskeleton – this can even be fatal. 

Why Do Freshwater Plants Need Calcium?

Calcium plays a pivotal role in producing plant tissues, enabling the plant to grow better. For example, the plant’s cell walls wouldn’t have been held together if it wasn’t for calcium. 

Calcium is also crucial in activating certain enzymes and sending signals that coordinate cellular activities. 

If a freshwater plant is experiencing calcium deficiency, the new leaves to grow will become twisted and stunted, whereas the tips of the leaves will wither. 

If you believe your freshwater plants lack calcium, the most likely cause is the use of RO water or soft water in the tank. It’s recommended to gradually increase the water’s hardness over a few days. 

Now that it’s established that pretty much any creature that goes inside your freshwater tank needs calcium in its system, let’s look at the ways to fortify it. 

But before that…

What Is The Best Freshwater Aquarium Calcium Test Kit?

We recommend using Fluval’s Calcium Test Kit, suitable for freshwater and saltwater tanks. 

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How To Add Calcium To Freshwater Aquarium?

Some ways of adding calcium to a freshwater aquarium are frequent water changes, adding supplements like cuttlebones, crushed corals, calcium blocks, and liquid calcium additives. 

I’ve listed and explained all of them below: 

  • Frequent water changes 
  • Cuttlebones
  • Chicken eggshells 
  • Calcium blocks 
  • Crushed corals
  • Crushed oyster shells
  • Wonder Shells 
  • Liquid calcium chloride 
  • Kalkwasser/Limewater 
  • Two-part solutions
  • Calcium reactor
  • Dietary calcium supplement 

Frequent Water Changes 

Depending on the water hardness level of tap water in your region, most of the time, you can achieve the desired calcium level by simply performing frequent water changes. 

There’s no brassbound rule dictating the right frequency and amount of water change to be performed, but the general practice is to change 25% water once every two weeks. 

No two aquariums are the same. Thus, the need for water change varies from one tank to another. Ultimately, it boils down to the size of the tank and stocking number. 

You should also be careful about not overdoing water changes, as this can lead to the destruction of good bacteria colonies and a spike in ammonia and nitrite levels. 

Be sure to test the calcium levels before relying on this technique or any other technique for that matter. 

The following are a few signs of high calcium concentration in water:

  • Difficulty lathering soap 
  • Tubs and showers are scummy and challenging to clean
  • Spotty and filmy dishes 
  • White crust near faucets, drains, and showerheads 
  • Skin is dry and squeaky after a shower 

These are some tell-tale signs of high calcium levels in the water. But the best way to know is to contact your local authority. They will tell you all about what minerals are available to what extent in your water supply. 

If you’re unable to reach them, another choice you have is to get your hands on something like this – USA-made Total Hardness Test Strips from Amazon or a nearby home improvement store.


Cuttlebones are easy, cheap, and effective tools to increase the water’s calcium concentration over some time. Highly porous, cuttlebones are large interior shells harvested from cuttlefish and contain about 85% calcium. 

The best part about cuttlebones is that they dissolve slowly in the water – thus, not changing the water parameters drastically or suddenly. 

And they’re not only teeming with minerals but also serve as aesthetic decorations. 

However, if left dunked in the water for long, cuttlebones are known to get mushy, decay, and produce a foul smell. 

And since cuttlebones are fairly big, you don’t want to add them whole. It will be an overkill. So instead, start by adding a small piece about 1 inch long. 

As cuttlebones float, you might want to weigh them down using pebbles or boil them first. 

Chicken Eggshells 

Chicken eggshells are a great source of calcium as they consist of calcium carbonate (98.2%) and a trace amount of other microelements like manganese, boron, iron, magnesium, silicon, sulfur, and zinc.

To prepare the eggshells, boil them for 5 to 10 minutes to get rid of bacteria. It’s also easier to remove the inner membrane once they’re boiled. 

Let the eggshells cool off and dry. 

Next, you can roast the eggshells in the microwave for 5-10 minutes to ensure there’s no moisture left. This step is optional. 

Add the eggshells into a coffee grinder and run it until they’re pulverized into powder. Add a couple of tablespoons of powdered eggshells as required once you’ve evaluated the calcium levels. 

If pulverizing the shells sounds like a hassle, you can add them without breaking them. But make sure you boil them first and remove the membranes. 

You can then remove the eggshells after a couple of days once they no longer add calcium to the water. It’ll only contribute to a foul smell if left for too long. 

Calcium Blocks 

Calcium blocks are concentrated calcium and magnesium pressed into a block form. Compared to cuttlebones, calcium blocks dissolve faster and alter the water hardness much quicker. Another advantage is that it will not cloud water. 

The blocks last in the water for around 2 weeks. It’s recommended to take out anything left after 2 weeks and add a new one. 

And lastly, although manufacturers recommend adding calcium blocks regularly, we recommend only using it as a luxury instead of a necessity. 

Crushed Corals 

Using crushed coral is one of the easiest ways out there to increase the calcium percentage in your freshwater aquarium. It doesn’t require extra work as eggshells do. Instead, simply add a layer of crushed coral at the bottom. 

Besides lending your tank a natural look, crushed coral substrate helps to cover the bottom glass completely. Otherwise, your fish might become disoriented due to unnatural reflections. 

While crushed coral definitely has a higher calcium concentration, it is also rich in salinity. Therefore, channel moderation when using it. Be especially careful if you have shrimps and snails in the tank. 

Crushed Oyster Shells 

Crushed oyster shells have a high calcium concentration, but at the same time, they’re also rich in salt content. Thus, you should only use them sparingly in a freshwater tank. 

That being said, they do make an attractive way of adding calcium to your fish tank, don’t they?

Wonder Shells 

Wonder shells are commercial and convenient alternatives to crushed coral and oyster shells. They last for about a month and improve the water quality while raising the calcium levels simultaneously. 

Even though they’re artificially made, wonder shells are easier to use and clean than crushed coral or shells. 

However, since they’re usually so concentrated, it’s best to start with small wonder shells one at a time.

Liquid Calcium

Available at most pet stores and online, liquid calcium additives like Brightwell Aquatics Calcion efficiently increase the water’s calcium concentration. 

However, liquid calcium supplement does come with some vices. For starters, it’s comparatively costly. Second, it is best suited for tanks with a lower calcium demand. And lastly, it can cause a drop in alkalinity over time, decreasing the water’s pH balance. 

While you can add the additive all at once directly, I prefer using the drip system. So here’s what you need to do:

  • Gather your supplies: an 8 oz water bottle, air tubing valve, flexible tubing, and a drill. You should use a plastic valve as the metallic ones will erode. 

  • Drill two small holes in the lid of the water bottle. The holes should be wide enough to allow rigid tubing to fit in place. 

  • Cut a piece of tubing at three-fourths the height of the water bottle. 

  • Position the piece of tubing in one of the holes in the lid. 

  • Attach flexible tubing to the outer end of rigid tubing. The length of flexible tubing should be enough to reach from the bottle to sump or the tank. 

  • Firmly attach the airline valve somewhere along with flexible tubing. 

  • Attach another 4-inch piece of flexible tubing into the other hole in the water bottle lid. 

  • Fill the water bottle with calcium chloride solution dissolved in tank water.

  • Tightly screw the lid onto the bottle and close lightly. 

  • Open the valve and blow into the 4-inch tubing length until water starts dripping from the longer tube. 

  • Close the valve and position it in the sump

  • Regulate the dial for your desired drip rate 

Now, the desired drip rate is subjective to factors like the tank’s size, stocking number, layout, etc. Make a habit of regularly checking the levels of calcium, in addition to pH and alkalinity. 

Adding too much calcium chloride will make the water acidic and over-concentrated with minerals. 

Kalkwasser/Lime Water

Kalkwasser is german for limewater. And it’s actually a blend of calcium hydroxide powder and reverse osmosis (RO) water or water with a high pH level. So besides increasing the water’s calcium concentration, it also has the added benefit of balancing the pH. 

Kalkwasser is easy to buy and comes at an affordable price. On top of that, it doesn’t lead to a foul smell or create any residue – quickly making it a favorite choice among fishkeepers. 

It’s pretty easy to prepare. It comes in just-add-water designs and contains only the ions you require. 

However, the main caveat of kalkwasser powder is that it is dangerous to inhale since it is a caustic substance. Also, keep in mind that it needs to be used the same day that it’s mixed, or else it will react with atmospheric carbon dioxide and become unstable. 

Two-Part Solutions 

Solutions like Two Little Fishies’ C-Balance balance the calcium level and pH simultaneously without altering any other parameter. 

It is sold in 2 half-gallon containers – one with solution A and another with solution B. According to the instructions, you first add solution A into the water and then add solution B. 

Calcium Reactor 

A calcium reactor consists of four parts: calcium carbonate or aragonite media that dissolves in water to release calcium, carbon dioxide that changes the pH levels to discourage or promote dissolution, a solenoid valve that opens or closes in response to electricity, and a pump that pushes water from the tank through the reactor. 

Besides controlling the tank’s calcium levels, calcium retractors also regulate the magnesium and alkalinity levels. It sits alongside the sump beneath the tank, taking in carbon dioxide from the tank and dissolving an interior piece of carbonate or aragonite. 

Here’s a link to an in-depth video on how to set up a calcium reactor:

Dietary Calcium Supplement 

If you have a fish-only tank, you need not worry much about their calcium requirements as most commercial food available in the forms of pellets and flakes are enriched with calcium, alongside several other crucial minerals. 

However, if you have inverts like snails that require calcium in their day-to-day lives, you can consider feeding them antacid tablets. The tablets will change the water’s color once dissolved but are deemed to be an effective and efficient solution for low-calcium environments.

Frequently Asked Questions 

Here’s a look at some of the most frequently asked questions on the topic!

Does Calcium Raise pH In An Aquarium?

Several parameters interact with one another in an aquarium. Therefore yes, calcium level increases water’s pH level, alongside alkalinity and hardness. 

Changing the tank’s calcium levels directly impacts all of these water parameters. 

On the other hand, if the tank’s pH level is too high, the calcium will not dissolve and hence will not act as a buffer stopping the water from becoming too basic. 

How Do I Give My Freshwater Snails Calcium?

You can dilute calcium supplements in the water and add them to the snail tank and feed the snail calcium-rich food like turnip greens, soybean, broccoli, and kale. 

How Much Calcium In A Freshwater Tank?

A standard freshwater tank should have a calcium hardness of around 70 to 90 mg/L (0.0009 to 0.012 oz/gal).

If the tank’s calcium concentration is higher than required, scaling will appear on the edge of the water surface. So it’s about time you buy a kit and check the parameters.

What Is The Best Source Of Calcium For Snails?

The best source of calcium for snails is a calcium-rich diet consisting of foods like cabbage, beans, turnip greens, okras, peas, spinach, kale, and soybean. However, it’s essential to enrich the tank’s water with calcium supplements every once in a while – especially after a large water change. 

But before you make any changes, whether it’s the calcium level or something else, always first check the parameters with a reliable kit.

Here’s a link to the one we recommend. 

Do Aquarium Plants Need Calcium?

Yes, aquarium plants need calcium, just like they need iron, phosphorus, potassium, and manganese. If your plant is experiencing calcium deficiency, the new leaves that grow will be twisted and stunted. Also, the tips of the leaves will wither. 

Calcium, as a crucial component of a structurally stable cell wall, helps in the plant’s cell wall production process.

The use of RO water or soft water in the planted tank can explain calcium deficiency.

How Do You Raise Calcium Hardness In A Fish Tank?

You can raise calcium hardness in a fish tank by adding calcium-rich substances like cuttlebones, crushed coral, Wonder Shell, and liquid calcium additives. 

Adding Eggshells To An Aquarium – Can It Be Done? 

Yes, you can add eggshells to an aquarium as it is a fantastic source of calcium. However, you first need to boil the eggshells to get rid of viruses, peel off their inner membrane, and pulverize them into fine powder in a mixture. 

You can also add whole eggshells without crushing them. But still, we recommend boiling and getting rid of the membrane first.

Adding Calcium To Planted Aquarium – How?

The best technique for adding calcium to a planted aquarium is to add calcium-rich supplements like calcium blocks, crushed corals, cuttlebones, Wonder Shell, and liquid calcium chloride. 

Final Words: How To Add Calcium To Freshwater Aquarium?

There are at least a dozen different ways of adding calcium to a freshwater tank. You can go all-natural by using substances like crushed eggshells and oyster shells or use readily available liquid additives like limewater, two-part solution, and liquid calcium chloride. 

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