A low carbonate hardness (KH) level allows pH levels to change rapidly, which may lead to health issues for your fish. Unfortunately, raising the KH level also increases the pH level.
Here is what you should know about raising KH without throwing off the pH level of your aquarium.
What Is the KH Level?
KH (carbonate hardness) measures the levels of carbonates and bicarbonates dissolved in the water. A higher KH reading means that the water has increased buffering capacity.
A high KH allows the water to neutralize harmful acids and prevent the pH level from dropping quickly. If the KH level in your aquarium is low, you are more likely to suffer from a sudden drop in the pH level.
KH is measured in degrees of KH (dKH) or parts per million (ppm). One degree of KH equals 17.9 ppm.
The ideal KH reading for a freshwater aquarium is about 4 to 8 dKH (70 to 140 ppm).
If your fish require a slightly high pH level, you may need higher KH. For example, a KH level of 10 dKH can help maintain a pH level of 8 to 9, which is ideal for African cichlids.
Can You Raise KH Without Raising PH?
Almost all methods for raising KH also raise the pH levels. Increasing the KH in the aquarium requires additional dissolved carbonates and bicarbonates.
Carbonates and bicarbonates are alkaline compounds. Both substances remove H+ ions and lower the acidity of the aquarium water.
The pH scale measures the acidity or alkalinity of your aquarium. A pH level of 7 is neutral. Anything lower than 7 is acidic and anything higher is alkaline.
The pH level increases as you increase the KH level. Unfortunately, natural methods of lowering pH levels also reduce the hardness, which brings the KH level back down again.
For example, adding peat moss or driftwood releases tannins that destroy the bicarbonates. Reducing the bicarbonates lowers the KH.
If you need to increase the KH in your tank, you can expect the pH level to increase. Instead of attempting to lower the pH level after adding carbonates and bicarbonates, allow it to gradually decrease through natural processes.
After achieving the optimal KH level and keeping up with frequent water changes, the pH should stabilize to optimal levels.
How to Raise KH in an Aquarium
Use any of the following methods to safely raise the KH in a fish tank:
- Add potassium bicarbonate
- Add crushed coral
- Add limestone
- Use dechlorinated tap water
- Use alkalinity buffers
As mentioned, each of these methods increases the pH level. However, the pH level should stabilize. To avoid a pH level spike, try to gradually increase the KH level a small amount at a time.
You can also wait until the pH level reaches the bottom of its healthy range. After raising the KH level, the pH level should not exceed the upper end of the range.
For example, most tropical fish need a pH level of 6.8 to 7.6. If you wait until the pH is 6.8, you can safely increase it to 0.8 without exceeding the safe range.
Use Potassium Bicarbonate for Higher KH
Potassium bicarbonate is an alkaline mineral and is often used as a substitute for baking soda. Potassium bicarbonate is sold as a powder. Adding about 2.5 to 3.5 grams of potassium bicarbonate per 100 liters of water should increase the KH by 1 dKH.
Use Crushed Coral or Limestone for Higher KH
Crushed coral, limestone, dolomite rock, and aragonite are commonly added to the bottom of fish tanks to increase KH. These substances increase carbonate hardness and the general hardness (GH) of the water gradually.
As the crushed rock or shell has a gradual effect on the KH, you can keep an eye on the pH levels. If the pH levels start to get too high, you can remove the crushed rock or shell.
Use Dechlorinated Water for Higher KH
Performing a 20% to 25% water change with water that has higher alkalinity should raise the KH and pH level of the aquarium water.
Use a standard fish tank tap water conditioner to dechlorinate tap water. Allow the water to rest 24 hours before performing the water change.
Use Alkalinity Buffers to Increase the KH
Store-bought alkalinity buffers can quickly increase the KH in your aquarium. Some alkaline buffers are designed to first increase the pH level before increasing the KH, which is useful if both levels are low.
If you only need to raise the KH, look for alkaline buffers that stabilize pH levels. The product raises the KH, which also raises the pH level. However, the release of chemicals helps bring the pH levels back down.
How to Maintain KH and pH Levels in an Aquarium
Maintaining a healthy KH level will help keep the pH level within the right range. Two main issues lead to lower KH levels:
- Overstocking the fish tank
- Not performing water changes
Overcrowding a fish tank causes the KH to drop, as the fish produce more acids that eat away at the bicarbonates and carbonates. The KH and pH levels also start to drop without regular water changes.
KH is depleted through the conversion of fish waste into ammonia, nitrates, and nitrites. Replenishing the water every 30 days helps keep the KH level up.
Maintaining an aquarium requires you to monitor the pH level and change the water occasionally. However, there are many other measurements that you should consider tracking, including the carbonate hardness (KH) level.
Raising the KH increases the pH level, as the hardness of the water depends on the presence of alkaline compounds. However, maintaining a healthy KH level makes it easier to maintain a good pH range.
Use crushed coral, limestone, dechlorinated water, potassium bicarbonate, or alkalinity buffers to safely increase the KH.
If you are worried about the pH level increasing when raising the KH, wait until the pH level is at the bottom of the safe range. After raising the KH, keep up with regular water changes to maintain a healthy aquarium.
I have a bachelor’s degree in Computer Information Systems and over 10 years of experience working in IT. I have a wife and two children and love taking them to the zoo to see all the animals. I grew up with dogs and fish and now have two dogs and two cats. I’ve also played guitar for almost 20 years and love writing music, although it’s hard to find the time these days.