Sodium bicarbonate in reef aquariums is frequently used to adjust the pH and alkalinity of aquarium water. Understanding the impact and effects of its use in raising pH and alkalinity is critical to avoid stressing the livestock in your tank, including fish, invertebrates, and corals.
The effect of sodium bicarbonate in aquariums is an increase in alkalinity and an associated increase in pH. The benefits of maintaining proper alkalinity in aquariums include the maintenance of proper pH levels for livestock and providing carbonate and bicarbonate for use by corals in saltwater reef tanks.
How to raise pH in reef aquariums with baking soda
You can raise pH in your reef tank with baking soda, but you must be careful that your adjustments are small to avoid stress on your fish and other livestock. Baking soda will cause an increase in alkalinity in your tank as well. Testing for both alkalinity and pH is necessary before and after adding the sodium bicarbonate solution.
Mixing baking soda with RO/DI or distilled water will create the solution you will add to your reef tank. You may choose to mix a larger batch, let’s say a gallon at a time, to use as a recurring/dosing solution. You can also mix it in small amounts to make minor corrections as required.
Baking Powder vs Baking Soda in a reef aquarium
Baking powder is NOT the same thing as baking soda. The key difference is that baking soda (better) is sodium bicarbonate with sodium, and baking powder is sodium bicarbonate with potassium (not better.)
Don’t make the mistake of using baking powder when baking soda is readily available. Additionally, you can turn baking soda into soda ash in your own oven!
How to Raise pH in Reef Aquariums with Soda Ash
If your pH is very low, a better solution than baking soda for raising pH is to use soda ash (sodium carbonate.) Soda ash will raise the pH pretty significantly without the initial pH lowering that happens with baking soda. For example, let’s say your pH is 8.0 or less; then the use of soda ash would be fine because the increase in pH would likely not exceed the recommended levels. However, if your pH were 8.1 or higher, then baking soda would likely be preferred.
Soda ash also requires mixing with RO/DI or distilled water to create the solution for dosing your tank.
Without trying to blind you with science (which is a good plan since I am definitely not a scientist), bicarbonate and carbonate reactions are different. Therefore they impact saltwater aquarium chemistry, especially pH, differently.
Randy Holmes-Farley has an in-depth scientific explanation of the chemistry here.
- The sodium bicarbonate (baking soda) ionizes, and the bicarbonate partially separates into carbonate and acid. This temporarily reduces the pH a bit. The abundance of bicarbonate causes some of the bicarbonate to become carbonic acid, and the pH rises.
- The carbonate (soda ash) ionizes and combines with the acid to form bicarbonate. The increase of bicarbonate and carbonate raises the pH.
I hope that made sense to you, I’m still confused!
DIY Method: Making Soda Ash from Baking Soda
Did you know that you can create your own soda ash by cooking baking soda in the oven? It’s straightforward to do at home.
- Preheat the oven to 300 degrees
- Thinly spread baking soda (sodium bicarbonate) over a cookie sheet. (How much you use will depend on the amount of solution you are going to mix.)
- Bake the sodium bicarbonate (baking soda) for 1 hour
- Remove from oven and mix with RO/DI or distilled water for use.
How much baking soda to raise pH and alkalinity?
Adjustments to pH and alkalinity should be made in small increments. I recommend you never adjust by more than 1 dKH in a 24 hour period. Some say up to 1.4 dKH is acceptable. Using sodium bicarbonate in your reef aquarium is an easy way to make major adjustments.
Keep in mind that a key to success in reefing is stability. Alkalinity, pH, or any other parameter experiencing large swings is going to disrupt (at the least) and potentially kill your livestock.
Whenever I adjust by 1 dKH, my coral starts to show a bit of unhappiness – and that’s the signal I use as my canary in a coal mine. It’s clear that in my tank, at least, adjustments over 1 dKH are not welcome by the livestock.
Nano Reef Adviser
Sodium Bicarbonate / Carbonate Calculator
Marine Depot has calculators here to help you determine how much bicarbonate or carbonate you need to add to your reef tank.
What Causes Low pH in a reef aquarium?
pH is always changing throughout the day in your aquarium. pH typically goes up during the day and drops each night. Therefore, chasing a certain pH value is a little bit of a waste of time. It is good to shoot for a range that is the healthiest for your fish, invertebrates, and corals.
If you are having low pH problems, it may be due to one of the following issues.
- Carbon Dioxide Levels: pH can drop if the area the reef tank is in has high carbon dioxide levels. Just the simple breathing of people and pets can build up the carbon dioxide levels in a tight or poorly ventilated space.
- This can frequently occur with increased people (guests/party) or if doors and windows are being kept closed due to the weather or seasonal conditions. Another source of carbon dioxide is the use of un-vented appliances using natural gas.
- Sometimes simply opening a window or door near the aquarium can have a positive effect on the pH. When that is out of the question, you can run an airline from the house’s exterior and into your skimmer.
- Running a refugium on an opposite light cycle to your display tank (e.g., at night while your tank is ‘asleep’) can help reduce the nighttime pH dip. The macroalgae in the refugium will use carbon dioxide as part of photosynthesis. This may reduce carbon dioxide build-up in the water column and thereby maintaining or raising pH.
- Low alkalinity can also lead to low pH: This can be overcome by adding more alkalinity. As mentioned above, this can be accomplished with sodium bicarbonate or carbonate. There are other alkalinity supplements as well.
What Causes High pH in a reef aquarium?
Usually, problems with elevated pH levels are a result of actions by the aquarist.
Typical reasons are adding too much alkalinity supplements and/or a deficiency of carbon dioxide due to adding/dosing limewater (e.g. kalkwasser)
What is alkalinity in a reef tank
Alkalinity can be difficult to visualize. One way to look at it is the interaction of ions that affect the buffering capacity of saltwater. This buffering can be described as the amount of acid required to lower pH to where bicarbonate turns into carbonic acid.
Alkalinity is measured in ‘degree of carbonate hardness’ (dKH.) The range for alkalinity that appears to meet the consensus in reef aquariums is between 8-12 dKH (142-215ppm .)
In your reef tank, alkalinity represents your tank’s ability to resist chemical change. That is a good thing for the livestock you are trying so hard to maintain.
Alkalinity is one of the key three (alkalinity, calcium, magnesium) needed to grow stony corals like LPS and SPS successfully. Managing these elements will provide stability to your tank and likely promote coral growth and colorization.
How to Raise Alkalinity in a Reef Tank with Baking Soda
When your choice for increasing alkalinity is to either add baking soda or soda ash, then that would depend on your pH, as mentioned above.
Raising alkalinity in a reef tank with baking soda is the preferred method when pH is toward the high side. This is because of sodium bicarbonate’s effect of temporarily lowering pH. If you were to use soda ash, the high pH would be exacerbated.
How to Lower Alkalinity in a Reef Tank
If you need to lower alkalinity, you can add carbon dioxide by increasing gas exchange at the water line through aeration. Pointing your return outlets or powerheads at the water line to create agitation will help substantially.
A more drastic step is to use an organic acid like vinegar. Vinegar can be added directly to the tank. Obviously, this should be done with caution to avoid large swings in alkalinity over a short period.
pH and alkalinity should be tested regularly. The testing frequency will vary from tank to tank, especially due to the amount of stony coral. LPS and especially SPS coral will take up alkalinity based on the amount of coral
Testing for pH and Alkalinity
If this uptake of alkalinity by your corals exceeds what can be replenished by regular water changes – then you will likely need to begin a dosing regimen. You may add limewater (kalkwasser) to your auto top off system, begin dosing 2-part additives, or both.
For established and stable reef tanks, you could get away with testing pH once a month and every two weeks for alkalinity. However, practically speaking, you should check pH every two weeks and alkalinity weekly at a minimum.
A cardinal rule in reefing is you don’t add anything to the reef tank you aren’t going to test for!
Nano Reef Adviser
If you are trying to dial in your alkalinity, you could be testing it every day until it is stable. This will be a constant adjustment if you keep making changes in the tank, so be advised!
Using Baking Soda to Clean a Fish Tank
As an aside, you can even use baking soda to clean old aquariums! You wouldn’t want to use it to clean active aquariums due to the impact on pH and alkalinity discussed above.
You can fill the tank with a baking soda solution to break down the dirt and grime, following up with a damp sponge. Mr. Clean Magic Eraser ‘ORIGINAL’ works perfectly! Just make sure it says ‘original’ to avoid adding any residual chemicals to the tank.
Rinse the baking soda solution from the tank before wiping the walls with the sponge to avoid the potential of scratching acrylic tanks. If your tank is glass, then you do not have to worry about baking soda scratching the glass at all.
Summary: Effects of Sodium Bicarbonate in Reef Aquariums
You can use baking soda or soda ash to adjust the alkalinity and pH in your reef aquarium.
- Baking soda (sodium bicarbonate) will raise pH after an initial small drop. This temporary drop in pH goes away in a few hours.
- I believe this makes baking soda the best choice if your pH is 8.1 or higher.
- Soda Ash (sodium carbonate) will raise pH immediately.
- I believe this makes soda ash the best choice if your pH is 8.0 or less.
- You can create your own soda ash at home by cooking baking soda in the oven.
- It would be best to use a calculator to determine how much sodium bicarbonate or sodium carbonate is required to adjust your alkalinity to your target dKH – for the water volume in your reef tank. (see links in the article above)
- You should perform parameter tests before (to determine current status) and after adjustments (see if you hit your target.)
Read my recent article and learn how to create a low maintenance reef tank – the easy way