How To Lower Alkalinity In Reef Tanks (3 Best Ways)

This is the complete guide in showing you how to lower alkalinity in your reef tank.

Alkalinity is one of the most important water parameters to test for and maintain in a saltwater reef tank. If you want your corals to look great and thrive, you need to ensure the alkalinity level is within limits.

If you are a reef tank owner, it’s important to learn the effects of high and low levels of alkalinity can have on your tank. More importantly, you need to know what to do in the event you need to adjust these levels to stay in the proper range.

how to lower alkalinity in a reef tank

If you need to lower the alkalinity level in your tank, slow and steady is the key to success. Large, abrupt changes are a recipe for disaster with a reef tank.

There are 3 methods that you can use to lower the alkalinity level in your reef tank.

1. Perform a water change

For most situations, completing a water change on your reef tank will lower the alkalinity level. I suggest doing a 20-25% water change every day while checking the alkalinity level. Ensure to use RODI water with 0 TDS and a high-quality salt mix for best results.

Normally changing the water each day for a few days will bring the levels down to normal. Like many things with saltwater tanks, water changes are the answer to most problems.

Small water changes each day will allow for slow and minor adjustments to your water parameters. A change of 1-2 dkh is normal.

If water changes are not enough and you need to lower the alkalinity level more,  check out step 2 below and try adding organic acid.

2. Add organic acid

A surefire method of lowering the tank’s alkalinity level is to add some organic acid like white vinegar. Vodka dosing is another option. This method works, but there are a few important points to pay attention to.

Using vinegar will reduce the alkalinity level but it is a temporary fix. Like putting a bandaid on it. In the short term, levels will reduce but then slowly start to increase. Water changes will be a more effective long term cure.

Vodka dosing will cause a drop in PH. This can be a huge problem if it drops too rapidly. PH should drop no more than 0.1 or 0.2 per day. Anything more than that can have adverse effects on your reef tank.

Vodka dosing can lead to algae outbreaks including cyano. Keep an eye on all water parameters while dosing.

If you decide to try white vinegar or vodka, ensure that you start very slow with small doses and increase it over time. The more water volume you have, the more vinegar you can dose. Here is a chart to reference. Please note that this is for reference only.


3. Wait it out

The next method is to simply wait and over time the alkalinity level will naturally lower each day as your corals use it up. If your alkalinity level is slightly above normal and it only needs to be lowered a small amount, this is your best option.

Depending on your coral stocking, the dkh level could drop as much as 1-2 per day. It doesn’t take long before the levels are back to normal.

The other advantage of this method is you won’t have a PH drop. Once the dkh is back to normal, continue your regular water change and dosing schedule to keep the dkh within limits.

What is alkalinity?

Alkalinity is the ability of your water to buffer the PH levels as acids are introduced to the system. Basically shows how effective the water is in the tank to neutralize acids and the effect it has on PH. Alkalinity is present in 2 forms. Carbonate and bicarbonate.

What should my alkalinity level be for a reef tank?

The proper level for alkalinity is between 8-12 dkh.

The most important factor is to maintain the level that works for your tank and corals. Don’t chase numbers. Prevent them from fluctuating up and down.

reef tank water parameters

Is high alkalinity bad for reef tanks?

Yes having high levels of alkalinity can lead to serious problems in a reef tank. Not only can it have health issues for your corals, but fish can suffer from it as well. Fish can be more susceptible to diseases as the higher alkalinity levels can dissolve their mucus layers.

It can also have negative effects on the fish’s breathing, can damage their fins, and if the dkh is too high, cause fish to die.

Another problem caused by high alkalinity is the fact that it affects your tank’s livestock ability to absorb calcium. In some cases, calcium can precipitate out of the water causing it to be unavailable for use. This will cause serious health issues including growth concerns for your livestock in the tank.

What causes the alkalinity level to drop in a reef tank?

The main reason that alkalinity will drop is due to everyday consumption from your reef tank. This is normal and the alkalinity must be replenished on a regular basis via dosing and water changes. Depending on your livestock, the dkh level can drop by 1-2 dkh every day.

Your corals are constantly pulling alkalinity out of the water which is used to build their coral skeletons. Coral calcification depends on proper levels of alkalinity as they absorb it. When corals consume carbonate alkalinity it reduces the amount of carbonate available to other corals and reduces the overall alkalinity, raises acidity, and lowers PH.

Another reason could be due to an increase of Calcium. High calcium levels will cause the alkalinity to drop. Levels over 500ppm calcium can cause this which affects the buffering capacity of your aquarium water.

What effect does baking soda have on alkalinity?

Baking soda is also known as sodium bicarbonate and it does have an effect on alkalinity. When you add baking soda to your reef tank, not only does it increase the alkalinity, but will increase the PH as well.

How to test for alkalinity in a reef tank

When testing the alkalinity level in your reef tank, it’s important that the test is accurate and precise. The best tester on the market today (in my opinion) is the Hanna Instruments alkalinity checker. Click the link to read my full review of the Hanna checker.