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How Much Crushed Coral To Raise pH?

How Much Crushed Coral To Raise pH

Adding crushed coral to your home aquarium or tank is an effective way to raise the pH level of the water, which is necessary to maintain an adequate acidity level for your aquatic life. In this article, we’re exploring how much crushed coral is necessary to begin to raise the pH level. 

On average, a tank requires up to a half-cup of crushed coral per 20 gallons of water to start raising the pH level. It causes a gradual pH change that can be seen over a period of several days to a few weeks. 

The rest of our guide will explore the specifics of using crushed coral to raise pH in home aquariums, including the time frame and measurements needed. We’ll also discuss when crushed coral becomes ineffective at a certain point, and whether or not it can also raise the GH and KH levels in a tank. Without further ado, let’s dive into it!

How Long Does It Take Crushed Coral To Raise pH?

When you add crushed coral to your aquarium tank, keep in mind that it won’t change the pH immediately. Crushed coral is primarily composed of calcium, which creates carbonic acid (calcium carbonate) when it reacts with tank water. This carbonic acid solution neutralizes the acid currently present in the water, thus increasing the pH level. 

Crushed coral works by essentially dissolving in the tank’s water, and the lower the pH level currently is, the faster the crushed coral will begin dissolving.

And this relationship works vice versa as well; as the pH level increases, the rate of dissolving decreases for the crushed coral. So, you’ll see most of the change occur at the beginning of the process, as the crushed coral exits the filter with the water.

On average, though, with the right ratio of crushed coral to tank water, you can see an effective increase in the pH level in just a few days. Typically, this process requires a gradual change lasting a few weeks. Most people recommend checking the pH level of your water every three days or so to gauge the acidity. 

At What pH Does Crushed Coral Stop Dissolving?

As previously mentioned, the rate of crushed coral dissolving in tank water will drastically slow down as the pH level increases. And at a certain point, the coral will stop dissolving because the water is too alkaline (basic), which causes the coral matter to turn into substrate. This typically occurs when the pH level in the tank reaches about 8.2 on the scale (alkaline).

Note that if you don’t want your water to reach that high of a pH level, you’ll need to slowly introduce the crushed coral in small amounts at first. You can sort of custom-adjust your water pH level by being intentional with the amount of crushed coral you add to the tank. 

When the crushed coral stops dissolving, you could have a problem on your hands if you chose to release the crushed coral via the water filter. In this case, it could potentially leave precipitate in the water filter and clog it, making it less effective at filtration. 

But if you’ve added the crushed coral to your tank by using it as substrate or manually adding it to the tank, you likely won’t incur issues with filtration when it stops dissolving. 

Does Crushed Coral Raise GH And KH?

Crushed coral is a pretty versatile substance to add to your home aquarium water, as it affects more than just the pH level. When it comes to the KH level in a tank, we’re talking about the number of bicarbonates and carbonates present. The KH level affects the neutralization of acid in the water and keeps the acidity stable. 

And when it comes to the GH level in a tank, we’re talking about the “general hardness” of the water. In essence, this relates to the number of magnesium and calcium ions in the water, which affects the health of fish, plants, and other aquatic life. 

Crushed coral can actually raise the KH level in your aquarium tank, effectively keeping stability in the water. Crushed coral can also raise the GH level in your aquarium tank, which increases the hardness level of the water and the amount of minerals present. 

This is something to keep in mind when using crushed coral, as it changes the whole equilibrium of the tank and living things housed inside of it.

How Much Crushed Coral Per Gallon Freshwater?

Depending on what you’re hoping to achieve, you will need different ratios of crushed coral to water in your tank. As a general rule of thumb, though, most people suggest using about ½ cup of crushed coral for every 20 gallons of freshwater in your tank. 

The thing is that most people want to closely monitor the pH, GH, and KH level changes, so you may start with just ¼ cup of crushed coral for every 20 gallons of freshwater in your tank. This roughly equates to about one pound of crushed coral per 10 gallons of water, if you’re wanting to measure by weight. 

If you’re adding the crushed coral manually to your tank (instead of via the filter), you’ll want to definitely start with a smaller ratio of about ¼ cup per 20 gallons of water. 

Keep in mind that any crushed coral in the form of substrate should be added first before you decide if you need to add more crushed coral via the filter or manually. 

Final Thoughts

When caring for a home aquarium, you’ll need roughly ¼ cup to ½ cup of crushed coral per 20 gallons of water in your tank. The process of raising the pH level is gradual, as the coral dissolves the fastest when the tank pH level is the lowest. 

The addition of crushed coral – whether via filter, substrate, or manually – also results in an increase in the GH and KH levels. These are all delicate factors to consider before adding crushed coral to your freshwater tank

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Erik Miller

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Hello, there. Welcome to my blog. I am Erik and I’m the main editor of Sealife Planet website.

My passion and hobby has always been scuba diving. My mission is to grow this website and help others with useful information about the sea world. Enjoy! is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to

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