How to Lower Alkalinity in a Reef Tank

How to Lower Alkalinity in a Reef Tank

As a reef tank owner, my top priority is ensuring that everything that lives inside my little water world is happy and healthy. Unfortunately, when I found out I had high alkalinity in my reef tank, I learned that it could damage my fish, my coral, and even my equipment. That was the last thing I wanted. So, with that in mind, I learned how to lower alkalinity in a reef tank and why it’s so important.

What is Alkalinity

Before we discuss how to lower alkalinity in a reef tank, it’s best to know what alkalinity it is and why it’s so important to monitor it on a regular basis. Essentially, the alkalinity is a measurement of how effectively the water in your tank neutralizes acids and how it impacts your pH. It tells you how much carbonate and bicarbonate is in the water and how your pH will stand up to additional acid in the tank.

Alkalinity is measured in degrees of calcium hardness or dKH. One dKH is equal to 17.86 milligrams of calcium carbonate per liter of water. Carbonate and bicarbonate are necessary for reef tanks because they help coral remain healthy and build a strong skeleton.

Effects of High Alkalinity on a Reef Tank

Water that comes straight from the ocean has an alkalinity of around 8 to 9 dKH, and that may be an ideal range for your reef tank too (but we’ll talk more about that in a minute). Once your alkalinity goes over 10 dKH, however, it’s generally too high and can cause serious damage if left unchanged.

For your coral, a dKH over 10 can cause the skeleton to grow faster than the tissue. It can also lead to discoloration. If you have fish in your reef tank, high alkalinity can dissolve the protective layer of mucus that protects them from bacterial and fungal infections. It can also cause breathing trouble and deformed fins and tails in your fish. Over time, high alkalinity can kill both your fish and coral.

When left untreated, high alkalinity can even damage your tank and equipment, such as heaters, pumps, and filters. This occurs when calcium builds up on these parts due to the elevated numbers, and the residue can burn out your motors. When the calcium builds up quickly on the equipment, it’s no longer available to the living organisms within the tank.

How to Test For Alkalinity

Because alkalinity plays such an important role in your reef tank’s health, it’s important to test it regularly. I usually recommend testing your alkalinity once a week, though if you’re having problems with it, you’ll want to test it more frequently. You can do this by purchasing an alkalinity test online or in pet or aquarium stores.

Test kits are available for every budget, ranging from basic to expensive ones that offer a digital reading. While every test kit is different, most of them require you to take a sample of your tank water and add a few drops of a chemical reagent that will turn the water a certain color. You’ll then use a syringe or dropper to add drops of a second reagent until the water reaches your desired color.

The number of drops of the second reagent you used typically provides you with your alkalinity measurement. No matter which test kit you buy, use it safely. Always follow the directions carefully, and avoid getting the chemical reagents on your skin or clothing.

Ideal Amount of Alkalinity

So, by now you are probably asking yourself, what should my ideal alkalinity be in my reef tank? As I mentioned before, the ocean has an alkalinity of around 8 to 9 dKH. You may want to keep your reef tank’s numbers within this range or a little lower. If you have fish, the ideal range is 7.8 to 8.3 dKH.

If you want the colors of your coral to really pop, you can even allow your alkalinity to drop below 7 dKH. If you can’t decide what to do, take a look at your coral. If they look healthy and thriving, you may want to avoid adjusting the alkalinity right now and simply monitor it for the time being but be sure to test at the first sign of any changes.

How to Lower Alkalinity

If you do have high alkalinity in your reef tank, there are some steps you can take to lower it. The most basic is changing your water regularly. Always replace your current water with reverse-osmosis water. Even changing about a quarter of the water in your tank daily for a few days can make a difference. However, if you do decide to completely change out all of the water, make sure whatever salt mix you use has an alkalinity of 8dKH or less.

For some reef tank owners, this is all you have to do to lower the alkalinity. For others, it’s not enough. Another easy method involves adding organic acid, like white vinegar, in small doses. Just keep in mind that this will lower your pH. You can raise the pH again by agitating the water’s surface with your pump. Again, only add a little each day, and retest your water before adding more.

If your alkalinity is just barely over the healthy range, you may want to wait it out before making any major changes. Simply having large healthy corals will lower your alkalinity naturally, and you may find yourself eventually having to raise the number with bulk additives, such as sodium carbonate (or soda ash) and sodium bicarbonate.

Final Thoughts

Owning a reef tank full of beautiful fish and colorful corals is a fascinating hobby, but it’s important to keep a regular check on your alkalinity. You can do so by purchasing an alkalinity testing kit and performing weekly tests to make sure your numbers are within the safe range.

If they’re not, there are a few steps you can take to lower your alkalinity. Just keep in mind that choosing not to lower the number can harm your fish and coral, and it can even damage your tank and its equipment.

We hope this article has helped you answer the question “How to Lower Alkalinity in a Reef Tank?” Please let us know your thoughts and any issues you have had controlling alkalinity in the comments below.

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