Crushed Coral

Crushed Coral – Everything You Need To Know

Crushed coral used to be one of the most important tools in a fishkeeper’s arsenal. While it has been replaced by other products on the market, a lot of people still swear by crushed coral, and this isn’t a surprise, really. It is affordable, and it can really help with overall tank conditions.

On this page, we are going to take a little look at what crushed coral is and, perhaps more importantly, what it does. 

What Is Crushed Coral?

Crushed coral is pretty much what it says on the tin.

It is crushed-up pieces of coral skeletons. There will also be some limestone and some shell in there too.

Crushed coral tends to be pretty coarse in terms of thickness, which is why it is still used in many aquariums. If you pour crushed coral into your tank, you don’t have to worry about swirling grains in the water if you have a particularly high-flowing pump. Crushed coral stays firmly rooted in place. 

What Is Crushed Coral Used For?

Crushed coral has a couple of jobs.

It is normally used when a fishkeeper wants to raise the pH of their aquarium. So, if you have an aquarium with water that is too acidic, then dropping some crushed coral in the water can up it. This is because bicarbonate ions in the crushed coral will dissolve in the water, changing up the water a little bit.

In addition to this, crushed coral can be used when the water is too soft. This is due to calcium ions in the crushed coral. This means that when the crushed coral is dropped into the tank, the hardness will start to rise.

Of course, if you get the right amount in there, then you will be creating the perfect environmental conditions for your fish.

Is Crushed Coral Good For Fish?

We are in two minds about this, as are most fishkeepers.

Obviously, the idea that crushed coral will allow you to balance the water for your fish is going to be fantastic. You want your fish to be swimming about in the ideal water conditions. This is how they thrive. Happy fish are good fish. We love crushed coral for this and, in our opinion, it is one of the easiest ways to start to tinker with your water chemistry.

That being said, there are some fish keepers out there that tend to avoid using crushed coral in their aquariums.

As we mentioned before, crushed coral does tend to be quite a coarse grain. When it sits at the bottom fo the tank, it is much more likely to trap old pieces of food, fish waste, etc. Even if you have animals that are trying to feed off of the bottom, they may not be able to get rid of all of this. This does mean that there could if you are unlucky, be a bacteria build-up in your tank. Obviously, this is something that is not going to be great for the fish in the slightest.

However, we think that the balance of the water is a huge benefit here. Even if there is the risk of bacteria, food, etc. getting trapped in the substrate, the risk is going to be minimal. It is something that you are not going to need to worry about all that much. Plus, there are easy ways to deal with that issue anyway.

It is also worth noting that those people who use a crushed coral substrate that do not regularly maintain their tank will often find an algae outbreak occurs. This may happen a year or two down the line, but it happens. If you are the type of person that often falls behind on the maintenance of the tank bed, then you may find that a sand substrate is a better option. Although, even that is going to have a couple of issues that you will need to deal with.

As long as you are not using so much of the crushed coral in your tank that it changes the tank in a way that is harmful to the fish, then you should be 100% fine.

Does Crushed Coral Raise GH?

As we said previously, crushed coral raises the hardness of the water. This means that it is raising the GH of the water.

Again, it probably isn’t going to be the best product on the market if you have incredibly soft water. However, if you do add some crushed coral substrate into your tank, then we are fairly certain that you will start to see the water hardness start to rise rather quickly.

Is Crushed Coral Good For Freshwater?

While crushed coral tends to work much between in saltwater aquariums, there is absolutely no reason why you can’t use it in a freshwater aquarium. In fact, a lot of top fishkeepers will use crushed coral in a freshwater aquarium.

That being said, you may be able to find better products to use in a freshwater tank. This is because if you have crushed coral, you will have to avoid using any of those animals that people normally use to filter the bottom of their tank (sand-filtering animals). Although, for some people, this is going to be perfectly fine. For the rest of the fish, you don’t really need to worry what is in there.


Crushed coral is a popular substrate for both saltwater and freshwater tanks.

Crushed coral is a substrate often used to help raise the PH and GH levels of a tank.

Crushed coral tanks can be a bit tougher to maintain, and many people have found that they have had to deal with algae outbreaks because of the crushed coral. However, assuming that you are regularly maintaining the bed of your tank, this shouldn’t be too much of a problem.

For the most part, having crushed coral in your tank is not going to pose any danger to any fish in there.