how much crushed coral per gallon of freshwater

How Much Crushed Coral Per Gallon of Freshwater: Let’s Find Out! 

Crushed coral is a great way to reduce the pH of your fish tank. The crushed coral forms a buffer solution to deal with the pH. However, too much crushed coral can be detrimental to your tank. 

So, how much crushed coral per gallon freshwater do you need? 

You can use crushed coral either as a substrate or add it to your filter. For substrate, using 20 grams per gallon is a good idea. For filters, you have to add based on your needs. There are a lot of other things you need to keep in mind about crushed coral.

This is only the gist of the crushed coral business. In this article, we’re going to discuss more adding crushed coral to your freshwater aquarium. Let’s begin!

Can You Use Crushed Coral in a Freshwater Tank?

So, you might ask, is crushed coral good for freshwater? 

Yes! Crushed coral is good for freshwater for a number of reasons. When used as a substrate, crushed coral helps maintain the pH of your freshwater for a long time. Thus, keeping you free from worrying about your tank becoming too acidic. 

What Does Crushed Coral Do in an Aquarium? 

As mentioned before, crushed coral helps increase and manage the pH of your tank. However, understanding the process is just as important.

The main ingredient of crushed corals is calcium. The calcium reacts with the water to form Carbonic acid which acts as a buffer solution. Whenever the pH reduces, the buffer solution reacts to neutralize the acid. 

In this way, crushed coral helps maintain the pH of your freshwater tank. However, you should keep the pH level in check. To do so here are some test kits that you can use. 

Now, crushed corals only dissolve when the pH is low. So you might wonder, will too much crushed coral be a problem?

Yes, just like anything else in your fish tank, the crushed coral is also a necessary evil. In case you have too much crushed coral in your tank as substrate. It will hamper the water flow due to its size. 

Also, food remains, dead bits of animals, and plants can get stuck causing it to smell bad. If you’re using it on your filter, too much could drastically affect your pH as well. So, it’s important to be careful about the amount of Crushed coral in your tank.

How Much Crushed Coral Do You Need?

Coming to the all-important question, how much crushed coral should you use? A lot of people struggle with the amount of crushed coral they need. The steps of adding crushed coral are different for these steps.

The amount of crushed coral you need for each process and their technicalities are discussed below- 

Used as a Substrate

The substrate is always an important part of the tank. Since it’s the base of your tank, your substrate determines the quality of your tank. Also, too much or too little substrate can be a big factor as well. 

It is recommended that your substrate is at least 2 inches deep. Otherwise, it can disrupt the flow of water in your tank. So, you have to keep that in check when placing substrate.


Generally, using ½ cup substrate per gallon is a good idea. Which means about half a pound of crushed coral per gallon. Calculate the amount based on the size of your tank and then set your substrate accordingly. 

You can determine the amount of crushed coral for any size of tank based on its size. Suppose, you have a 55-gallon tank. Then, how much crushed coral for a 55-gallon tank?

If you have a 55 gallon tank, you can use around 30 cups of crushed coral. Which equates to roughly 30lbs of crushed coral. However, it’s important that you place the substrate first before putting anything else.

In some cases, you might need to give your pH a boost even with crushed coral as a substrate. Then you have to put the crushed coral in your filter as a quick boost.

In case you’re wondering how much-crushed coral you need for your tank. Here’s a table showing the more common sizes of aqueon tanks-

You can follow this table to help you determine the amount for you.

Used in Filter

Using crushed coral is a great way to deal with the increasing pH in your tank. Although it’s a bit more complicated, it can be a great way to keep your tank steady. 

Generally, you can put an amount of crushed coral in your filter. It will dissolve whenever your pH is out of balance. So, it’s a gradual process that can take up to a few weeks. 

For this reason, we recommend adding ½ cup per 20 gallons of water. Put the amount of crushed coral in your filter and place it in your tank. Check the pH every few days to see the change. 

If you don’t get the required change, add ¼ cup per 20 gallons each week. Continue until you get the required change. Although it’s a bit time-consuming, it’s worth the effort.

However, you need a good quality filter to make sure the crushed coral dissolves well. If you’re looking for a good filter for your tank, here’s our recommendations

These are some of the best filters for freshwater tanks we could find. 

To help you understand the amount of crushed coral you need, check the table below: 

TimeAmount Needed Per Gallon
Initial ½ cup per 20 gallons of water 
Once a week until attaining required pH¼ cup per 20 gallons of water 

However, once you reach the required amount of pH, stop adding crushed corals immediately. If you have any coral left in your filter, remove them as well.

Used Manually

You can use crushed coral manually on your aquarium as well. However, this process is only for emergencies. 

If you want an easy pH boost, simply take a handful of crushed coral. And place it in your aquarium. But do make sure the amount isn’t more than ¼ cup. Because you don’t want to mess up the pH level of the water. The coral will mix with the aquarium and get to work.

However, be careful that you don’t add too much. Not only will it risk a drastic increase in pH, it can also make your tank dirty and mushy.

Factors Affected by Crushed Corals 

Now that we know the need for crushed corals in our freshwater tank. We also need to know the technicalities as well. A fish tank is a complex process where everything you put, relies on others. 

From the lighting of your planted tank or the flow of water, everything relies on each other for stability. So, knowing how the crushed coral in your tank responds to everything else is important. 

Here are a few factors that you need to keep in mind before putting crushed coral in your tank-

Carbonate Hardness

Carbonate hardness or KH is the amount of carbonates and bicarbonates dissolved in the water of your tank. This refers to the amount of acid it can neutralize before the pH of your tank is changed.

However, you need to keep in mind that crushed coral doesn’t directly affect the pH of your tank. It increases the number of Calcium Carbonates in your tank, thus affecting its kH. Then, the kH is used to change the pH of your tank.

So, knowing the amount of kH in your pond is crucial when it comes to determining the amount of crushed coral. To answer your question- how much-crushed coral to raise kH?

It’s important to know that the higher the KH, the less likely is your pH supposed to change. So, try to have a KH as high as possible. If your KH reduces below 4.5, you need to start adding crushed coral based on the size of your tank.

Aquatic Plants 

Plants are an integral part of any aquarium. They drastically change the design aesthetic of your tank. Also, they are important for the stability of your plant. They help provide oxygen, increase filtration and promote algae growth.

Thus, knowing how to take care of plants is important but something we often forget. If the pH of your tank increases drastically, it can affect the plants for the worst. When you add crushed corals you need to keep that in mind. 

Adding too much crushed corals at a time can drastically change the pH. Eventually making it hard for your plants to survive. So, keep that in mind!

Generally, aquatic plants require a pH of 6.5 to 7.5. However, if you want a higher pH, make sure your plants will survive that. 


Just like plants, fishes also require a fair bit of attention when it comes to the pH of your tank. So, if you’re planning to increase the pH of your pond, make sure your fishes will be accustomed to the new pH. 

Furthermore, crushed corals are especially beneficial for certain fishes. Generally, they are accustomed to high pH. Also, they benefit from the environment created by crushed corals. 

Fishes like shrimp, Ebi, and cichlids are some of the most common fishes that benefit from crushed corals. If you have these fishes in your tank, it’s better to have crushed corals as the substrate. 

Source: Reddit

However, there are many fishes that often struggle with high pH. Also, smaller fishes can get stuck in the substrate if the grains of your coral is too big. So, keep these factors in mind before having crushed coral in your tank.

If you have burrowing fishes, snails, or turtles in your tank, crushed coral is a massive no for you. The grains of the crushed coral make it harder for them to move around in the bottom. Thus, risking injuries and damage. 

Presence of Detritus 

This is a two-edged sword for your tank. On one hand, the grains of corals are fairly spacious. As a result, they often trap remains of dead plants and fishes. Since they trap the detritus, they aren’t floating around. So, gives you a fresh and clean-looking aquarium.

However, as the dirt keeps accumulating at the substrate, it gets mushy. As a result, cleaning is a nightmare. Which is both labor-intensive and time-consuming.

So, you might ask, how to clean used crushed coral?

Although labor-intensive, the process of cleaning crushed coral is actually pretty simple. Siphon the coral with a vacuum and remove as much detritus as you can from it. Then rinse it clean and you’re good to go!

If you’re okay with the effort, crushed coral is worth it! However, if the vacuuming and cleaning feel like too much effort, it won’t be a great experience for you. 

How to Add Crushed Corals into Your Tank 

Now that we’ve discussed everything, let’s discuss how to put the crushed coral in your water. You can put crushed coal both as substrate and through your filter. The steps are-

Adding Crushed Coral as Substrate: 

If you plan to use crushed coral as your substrate, make sure your tank is empty. Afterward, take your crushed coral and place them at the very bottom of the tank. Spread it accurately and there’s no gaps or uneven parts there.

Also, you can add gravel, rocks, etc. with the coral to give your entire tank a better look. Once the substrate is placed, plant your aquatic plants and finally fill up your tank. Aquatic plants like dwarf hairgrass might die if the substrate isn’t made properly.

Adding Crushed Coral in an Established Tank

For people with a tank who need a pH boost, adding crushed to an already established tank coral is fairly simple. 

The most common way to add crushed coral is through the filter. Measure your coral carefully and give it a rinse. This will wipe off any dust and dirt from the crushed corals, making them ready for the filter. 

Also, you can simply add the coral on top of your tank and let it dissolve. Although it’s quicker, it can make your pond become mushy and dirty.

Afterward, just place them in the designated part of your filter and you’re good to go!

Tips for Using Crushed Coral 

If you’re using crushed coral for the first time, you need to keep a few things in mind. Otherwise, you risk causing more harm to your tank than good. Tips include-

Be Patient

The most common problem for most people trying crushed coral is that they add too much. Generally, crushed coral takes a bit of time to set and change your pH. But, oftentimes, people put too much at once for a quick change.

This causes the pH to change drastically and damage the flora and fauna of the tank. So, always be patient with your crushed coral. It can take a few weeks for your coral to get set, so keep that in mind. 

Replace Them in Time

Although crushed corals last a fairly long time, they won’t last forever. If you see your pH falling, it’s due to your crushed corals disintegrating. However, they don’t take a long time to start disintegrating once it starts. 

So, if you see your pH falling, take action immediately. Not adding more corals or changing them could drastically affect your pH.

With that, we’ve discussed everything you need to know about crushed corals. And we’ve shown steps on how to use them in your aquarium! 


How often do I need to replace my crushed corals? 

Although there’s no fixed answer, it generally lasts six months without any hassle. However, if you see your pH dropping abruptly, change it immediately! 

Can you mix other things with crushed coral as the substrate? 

Absolutely. You can mix things of similar texture such as gravel with the corals. However, mixing sand or similar material will only make the tank cloudy and hard to deal with. 

Can I put crushed coral in a canister filter? 

Yes! You can put crushed coral in a canister filter. However, don’t fill more than 25% of the filter with coral as it will result in a lot of waste and residue. 

Final Word

If you’re an aquarium enthusiast, finding the best materials for your freshwater tank will always be a priority. Crushed coral is one of the most common, yet useful materials in an aquarium. 

However, the amount of crushed corals has always been an issue. So, we tried to answer the all-important question, how much crushed coral per gallon of freshwater? 

We hope we’ve helped you!

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