Can I Use Crushed Coral In Aquarium?

A few people keep aquariums to add to their home aesthetics, while others own a tank because they adore different fish species. Whether you belong to the former or the latter category, interacting with fish in an aquarium has undeniable health benefits.

A 2019 study reveals that individuals who interact with aquarium fish experience alleviated anxiety, stress reduction, relaxation, and more.

Choosing the appropriate substrate is crucial if you plan to keep one in your happy place. Whether you want to go for a freshwater tank, reef tank, or saltwater aquarium, you have many options—crushed corals, dead corals, Star coral polyps – to name a few.

Homeowners new to a marine setup question if they can add crushed coral in the tank. While it does offer benefits, you need to be cautious about a few things.

What Is Crushed Coral Anyway?

Crushed corals are one of the most commonly used aquarium substrates consisting of limestone, coral skeleton pieces, and shell. 

Generally, strong water flow breaks large grain substrates, leading to unwanted debris buildup in your tank. 

Nonetheless, crushed corals save you from this vexing issue. As the name implies, the crushed corals are refined grains – unlike the larger ones. Not only are they a right fit for aquariums with strong water flow, but they also maintain the aquarium aesthetics. 

Benefits of Adding Crushed Coral In Freshwater Aquarium

If you aren’t familiar with the marine world, here’s something you must know.

Fish, like other animals, need a suitable environment to thrive. So, the story doesn’t end after you add water to your tank. 

Note that the fish living in a natural habitat is exposed to essential nutrients needed for survival. An aquarium, however, is an artificially created marine life – deprived of the appropriate water parameters.

Therefore, you need to consider several factors when maintaining an ideal environment for your fish pet. One, for instance, is the water’s pH.

Maintaining optimal pH levels is crucial to the well-being of the fish. Unfortunately, food leftovers, decaying organic matter, and other biological factors significantly drop the aquarium’s pH levels, posing a threat to marine life. Luckily, crushed corals containing calcium carbonate help boost an aquarium’s water pH level.

Crushed Corals – Ideal for African Cichlids

Different fish species have varying water requirements. Simply put, not all fish need a high pH to survive. Some, on the other hand, require optimal amounts to thrive.

For instance, African Cichlids, a saltwater fish, requires highly alkaline water, and crushed corals perfectly cater to their needs.

The calcium in crushed coral dissolves in water, enhancing the hardness and boosting the alkalinity and pH.

Therefore, anyone wanting to keep African Cichlids should go for crushed corals without a second thought.

Things to Consider When Adding Crushed Corals

Because crushed corals benefit marine life, it doesn’t indicate you can add a handful just like that. Aquarium owners must familiarize themselves with the technicalities associated with corals.

In fact, anything added to a freshwater aquarium affects the stability of other things. For instance, an inappropriate coral level can be detrimental to marine life.

So, here are a few things you must know before adding crushed coral to your water tank.

The Grain Size

Crushed corals, like other coral types, come in varying sizes. However, experts recommend adding small-gain corals. Here’s why.

Large grain corals follow up with a few issues. For instance, fish food leftovers and excrement settle down, trapping in the grains. This requires you to maintain the sand bed regularly.

Delaying the cleaning of freshwater tanks breaks down the detritus (excrement), releasing ammonia, nitrates, and phosphate into the water.

Unfortunately, these compounds destroy your tank aesthetics.

On top of that, you’ll be restricted to keeping only a few fish types minus the stunning sand-sifting species. The gorgeous-looking Gobies and Starfish tend to bury themselves in sand and sieve to eliminate coarse particles, serving as an ultimate cleaning force.

Adding large grain crushed coral prevents the specie from doing what they are good at while equally benefitting you.

Marine Plants

Aquatic plants are a luxury for fish that live in their natural habitats. Aquarium owners, however, take measures to provide a similar environment to the fish they keep in the tanks.

Plants enhance the fish tank aesthetics, boost filtration, provide oxygen, and encourage algae growth.

Regardless of the grain size you choose, you must add crushed corals in a controlled amount. When the pH level increases more than needed, it adversely affects the aquatic plants. 

Boosting pH levels drastically can make it challenging for the plants to survive. Ideally, marine plants need 6-7 pH. If you plan to keep fish that require more pH, you better opt for plants that survive a higher amount. 


Fish, like aquatic plants, also require attention regarding pH levels. If you are adding crushed coral to your fish tank, give your fish time to get accustomed to the new compound. 

Adding loads of crushed coral in the first go is certainly not wise. Instead, begin with smaller amounts; you can always increase the quantity later. 

Additionally, it is imperative to understand that crushed corals are advantageous for particular fish specie – consider African Cichlids and Ebi.

If you plan to keep other fish types, you better limit the usage.

Calcium Carbonate Hardness

Calcium carbonate hardness, kH, refers to the amount of carbonate and bicarbonates mixed in your aquarium’s water. It implies the acid amount it can neutralize before changing the pH levels. 

Note that crushed coral does not directly alter your water pH levels. Instead, it boosts the Calcium carbonates in the water, affecting carbonate hardness, consequently changing the freshwater tank pH levels. 

Therefore, you must know the amount of carbonate hardness minerals to determine the appropriate crushed coral amount. While you might assume they both go hand in hand, it’s quite the opposite. 

Simply put, higher carbonate hardness reduces the chance of altering the water pH. Therefore, it is best to keep the carbonate hardness high. Of course, you do not want to increase the pH levels beyond the safe amount.

As soon as the kH drops to 4.5, add crushed coral based on your aquarium’s size. 

What’s the Appropriate Amount of Crushed Coral?

High levels of crushed coral are neither safe for the aquatic plants nor beneficial for the fish. Therefore, it is essential to know the right amount suitable for marine life.

We’ll discuss the crushed coral required for different processes below.

Using As a Substrate

Because the substrate is the base of your freshwater tank, the quality of your aquarium is primarily determined by it. A substrate more – or less – than the needed amount can significantly impact aquatic life.

Experts recommend keeping substrate two inches deep – not more, not less. This amount ensures optimal water flow and avoids unwanted disruption.

You can use half a pound per gallon or 1/2 cup of crushed coral. However, calculate the tank size to determine the right substrate amount.

Of course, the substrate amount will be different for varying aquarium sizes. For example, a 30-gallon tank would require less substrate than a 50-gallon tank.

Further, make sure you put substrate before anything else in the tank.

As a Filter

Crushed coral maintains your water pH levels – as long as you use the right amount.

When you place a particular amount of crushed coral in the filter, it dissolves whenever the pH is imbalanced. This process happens gradually and can take a few days.

Therefore, it is best to add 1/2 cup of crushed coral per 20 gallons of water. Simply, put it in your filter and place the filter in the tank.

Ideally, check the water pH levels every week to determine if it alters. If you do not notice any change, consider adding 1/4 gallons every week.

Continue the process until you achieve the desired pH level. Yes, the process takes time and patience, but it’s worth it. The effort keeps your fish healthy, and your aquatic plants thrive well.

While your hard work will pay off, make sure you purchase a quality filter to ensure a seamless process. A substandard filter will not dissolve the crushed corals well, wasting your time and effort.

If you invest in a quality filter in the first go, it will complement your painstaking efforts by expediting the process of balancing tank pH levels.


The manual method comes in handy for emergencies. Adding a handful of crushed coral gives a quick pH boost.

However, be vary not to add more than 1/4 cup. Otherwise, it’ll mess up water pH, making your tank unsightly.

Can You Add Crushed Coral to the Tank?

It all comes down to this: Is it OKAY to add crushed coral to freshwater tanks?

Luckily, yes, you can add crushed coral to your aquarium. In fact, it was one of the sought-after substrates back in the day. Essentially, saltwater aquarists used it to balance water pH levels.

Over time, new products replaced the crushed coral. Because the latest alternatives ensure reduced excrete trapping and a quicker pH balance process, more people opt for them.

If you can dedicate yourself to regular tank maintenance, there’s no reason not to go for crushed coral.

Final Words

There are 101 reasons to keep an aquarium in your house; it enhances your home aesthetics and provides a sense of relaxation.

Taking care of fish makes up for a meaningful hobby to alleviate the rising stress levels.

However, you must get familiar with the appropriate water chemistry and parameters to maintain marine life. Doing otherwise will be deleterious to fish and plant health.

Because experts do not support the idea of adding dead coral to the tank, many marine enthusiasts are dubious about the usage of crushed corals.

Fortunately, they are safe – as long as you add the right amount.