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How to safely raise the pH in your fish tank

You tank water is considered to be hard and alkaline when it measures at above 7.0 in the pH scale. If you want to raise the hardness in your aquarium, you can follow this guide to find the best and most efficient way to do so.

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What determines the pH level in your fish tank

Most of the things you put in your fish tank will affect the pH of your waters. The first is your tap water, or wherever you got your source water from. You should keep in mind that your source water will vary occasionally due to changes made to the treatment facilities, seasonal swings and more. We recommend testing your source water at least once during the Winter, Spring Summer and Fall Seasons to see if the pH level has changed.

Your substrate can also change your water parameters. Planted soil is usually more acidic while corals/lime stones will give you more alkaline waters.

Last but not least, your bioload will also lower the pH. The higher the amount of wastes are being produced by your fish, the more acidic your waters will become over time. Your bioload also includes uneaten fish food. So, if you are overfeeding your fish, you should remove the leftovers and feed less in the next meal to prevent your waters from getting more acidic.

Aquarium fish that can live in high pH water

Most livebearers prefer living in alkaline waters. These include Guppies, Mollies, Platies and Swordtails. Paradise Fish, Africa Cichlids and some South American Cichlids also enjoy living in a high pH environment.

With that said, a vast majority of aquarium fish can adapt to whatever pH you have in your tank. If you still want to make your water more hard, you can take the methods we outlined below:

Raising pH at safe levels

Before you start trying to raise the pH of your aquarium, it is important to note that changing the alkalinity of your waters too quickly could cause your fish to go into pH shock. The sudden change could cause discoloration, loss of appetite, lack of activity and, if not addressed in a timely manner, eventually death.

So you want to be careful when it comes to changing your pH. The general rule is not to increase or decrease by more than 0.2 on the scale over a 24 hour period. When making adjustments, mare sure to test your waters soon after the additives are put into your tank.

How to raise pH without any additives

Water Changes

If your tap water, or where you are getting new water from, has a higher pH than your tank water, then you can raise your alkalinity by doing a simple water change. Of course, if you have already been doing regular water changes with no effect, you can try increasing the frequency of doing the changes as well as the amount of volume being swapped out (although we recommend that you don’t do more than 50 percent over a 24 hour period so that you won’t stress out your fish).

More aeration

You can also make your pH go higher by having more aeration in your tank. By agitating the surface of your waters, you will encourage more gas exchange, which includes removing carbon dioxide from your tank. As a result, your fish will live in a slightly more alkaline environment.

How to raise pH with additives

There are a few ways to raise the pH of your aquarium. You can find a list of our recommendations below:


API has a commercially available product that will increase the pH of your waters. Commercial products are somewhat controversial in that they can raise the alkalinity too much, too soon. So you want to follow the directions closely if you want to use pH Up.

For a 25 gallon tank, you should add 1/2 teaspoon. For a 50 gallon tank, you need to add 1 teaspoon. You should also keep in mind that it is safer to under-dose than to overdose, so you may want to start off with adding less than the recommended dose if you want to be extra cautious.

If you are interested, you can purchase the API pH Up with this link on Amazon (#CommissionsEarned).


You can also use cuttlebones to increase the pH level of your fish tank. To find out how to do so, you can check out this tutorial.

Crushed Corals

Another way to raise pH is with crushed corals. If you water gets too acidic, the corals will begin leeching into the water column, which will then raise the pH back up and keep it stable.

Crushed corals can be used as a substrate in your aquarium. With that said, the sharp edges could potentially damage the fins and other body parts of your bottom dwelling fish (such as Corydoras, Loaches and Plecos). If you have those types of fish, then we recommend that you put the corals in your filter. Alternatively, you can also use a filter media bag to hold the substrate and put it in your tank near your filter intake.

You can buy the CaribSea Crushed Coral on Amazon. (#CommissionsEarned).

Baking Soda

Baking soda will also work. With that said, you should be cautious as, similar to the aforementioned pH Up, you can easily overdose. The general rule is to use one teaspoon for every five gallons of water in your tank. We recommend adding slowly and testing your water soon after to prevent any sudden, significant swings to your water parameters.

You can purchase the Arm & Hammer Pure Baking Soda via this link from Amazon. (#CommissionsEarned).


One last method we recommend trying out is limestones. These rocks will leech calcium carbonate into your waters, resulting in harder parameters. You can find lime stones at your local hardware and/or garden stores.

You can use the stones as a substrate or as filter media. Similar to crushed corals, you can also but the rocks into a filter media bag and place it near your filter intake.


Cichlids and Live-bearing fish prefer living in hard and alkaline water.

You can raise the pH of your water though API’s pH Up, crushed corals, baking soda and lime stones.

If you decide to use pH Up or baking soda, we at Aquarium Blueprints recommend adding them to your aquarium slowly or you risk stressing your fish with a sudden and significant pH spike.

You can use crushed corals and lime stones as filter media, substrate or place them in a filter media bag inside your tank.