What Should KH Be In Saltwater Tanks?

What Should KH Be In Saltwater Tanks?


To maintain a healthy saltwater tank, you must keep your water parameters in check. There are several different levels that you want to check regularly and KH or Alkalinity is one of them.

The key to your success with keeping a reef tank long term is consistency. You want to avoid the water parameters from fluctuating and always strive to keep things consistent.

The proper level of KH in your saltwater tank should be between 8-12 dkh or 142 to 215 ppm.


alkalinity level for reef tank



What is Alkalinity?


The alkalinity of water can sometimes be confusing to understand but if you think of it in basic terms it makes a lot of sense. This is the Utah State University definition. “Alkalinity is water’s capacity to resist acidic changes in pH, essentially alkalinity is water’s ability to neutralize acid. This ability is referred to as a buffering capacity.”

So think of it as the buffering capacity of the water in your tank. It directly affects PH and refers to how much acid can be added to the water before a large PH swing takes place.

Difference between KH and GH

You should know that KH (Carbonate Hardness) and GH (General Hardness) are not the same things.

KH – The measure of carbonates and bicarbonates dissolved in water.

GH – The measure of magnesium and calcium dissolved in water. If you test your home tap water and say you have hard water, that would be referring to the GH.

KH and GH are 2 different water parameters to check in our tank done individually.


Alkalinity test kit


When you test the KH level in your saltwater tank, it’s important to use a good quality test kit. This will ensure an accurate result every time you use it and prevent errors from being made trying to correct a faulty reading.

If you have been in the saltwater aquarium hobby for a while, you know that maintaining a proper KH level is one of the most important factors to a successful reef. The more sensitive corals like SPS will appreciate a stable KH level.

Testing for KH can be done

My favorite alkalinity tester is the Hanna Instruments checker. It is a high-end tester that is reliable and accurate without the high price tag. I recently did a complete review of my Hanna alkalinity tester and you can read that by clicking the link or image below.


hanna instruments alkalinity checker review


How do I raise KH in a saltwater tank?


If your KH is low and you are looking to raise it, the first thing to do is a water change with a high-quality salt. The salt will have the necessary trace elements to help raise the KH level. A great salt to use is Red Sea Coral Pro.

Most times maintaining a good water change schedule will be enough to maintain or raise the KH level. But if it doesn’t, you can look at dosing 2 part calcium and alkalinity. There are different buffers that are available. Red Sea Reef Foundation B is a very good product.

Adding sodium bicarbonate (baking soda) will also raise KH level.



What happens if the Alkalinity is too high in a reef tank?


There are a variety of problems that high alkalinity can present. A reading greater than 12dkh is too high. It increases the chance of precipitation of calcium carbonate on your pumps, heaters, and other equipment causing them to become inefficient and fail over time.

It also causes hard corals and coralline algae to grow faster since not getting enough carbonate can be a rate limiting step in skeletal growth also known as calcification.

SPS corals in a tank with high alkalinity may suffer burnt tips. This is directly related to coral tissues being unable to keep up with the skeletal growth. Tissues will end up being more susceptible to burning by high light/UV levels.

Fish can suffer


High alkalinity can cause some aquarium fish to suffer and have serious health problems. If the alkalinity remains high over a long period of time, it can damage their protective mucus layer leaving them more vulnerable to bacterial attacks and infections.

If the water in your tank is too alkaline, this can cause non-toxic ammonia to become toxic and the fish will struggle to breathe. It can also have serious negative effects on their growth and lead to death if the high alkalinity level is not corrected.

Impact on Calcium


Another problem with a high alkalinity level is that it can interrupt the uptake of calcium by the corals. If the alkalinity is too high, calcium may precipitate out of the water becoming unavailable to others causing a negative impact on growth.



How do I lower KH in a saltwater tank?


If you find yourself in a situation where your KH level is too high, there are a few ways you can lower it.

The first thing to do is perform a water change with a high quality salt that can actually lower the KH. Not all salts are the same with respect to the amount of alkalinity it contains. Water changes will generally work well and not other actions are needed to lower the KH.

You can see the alkalinity contained in the Red Sea salt in the chart.




Naturally over time, alkalinity will drop as your corals use it up every day. So you can just wait a few days and test to see if the proper KH has been reached. If it has, adjust your dosing to maintain that proper level.

Lowering the KH can also be done by organic acid or vinegar dosing. This will immediately reduce alkalinity. But keep in mind that dosing your tank with vinegar can have a lowering effect on your tank’s pH level.


Why does the Alkalinity drop?


The most common reason why alkalinity drops in a reef tank is due to the corals using it up on a regular basis. Depending on the tank, your corals will use up 1 or 2 dkh per day. So it’s normal for alkalinity to drop naturally. Water changes are the best way to maintain the proper KH level.

If the calcium level in your tank becomes too high, say over 500 ppm, it is common for the alkalinity to drop.


Reef tank parameters chart


There are many other water parameters that you should maintain on a consistent basis. Here is a chart to reference.