Having a backyard pond can be a fun and relaxing way to add some natural beauty to your outdoor space. And what pond would be complete without some fish swimming around to admire? But caring for pond fish also means maintaining proper water conditions. One question pond owners often have is whether baking soda can be used safely in their ponds, or if it will harm their fish.
Below we’ll take a closer look at using baking soda in ponds with fish, including the benefits and potential risks.
Why Use Baking Soda in a Pond?
Baking soda, otherwise known by its chemical name sodium bicarbonate can be helpful for regulating pH levels in ponds. The ideal pH range for most fish species is between 6.5-8.
pH is a measure of how acidic or basic the water is ranging from 0 (very acidic) to 14 (very alkaline/basic). Most fish prefer a pH that is slightly alkaline rather than acidic.
Baking soda has an alkaline pH of about 8 when dissolved in water, Adding small amounts of baking soda can safely increase pH levels in ponds when needed,
Stable pH is crucial for fish health. Fluctuating pH causes stress and makes fish more vulnerable to disease. Ammonia and nitrites, toxic to fish, are also more prevalent at lower pH levels.
In addition to pH regulation, baking soda can also help:
- Reduce the toxicity of metals like aluminum, zinc, and lead in the water
- Neutralize humic acids
- Improve the efficiency of some medications used to treat fish diseases
So when used properly, baking soda has some legitimate benefits for ponds with fish. But the keyword is “properly” – since too much baking soda can be dangerous.
Dangers of Using Too Much Baking Soda
While baking soda clearly has its uses, it’s important to exercise caution. Excessive amounts of baking soda can cause pH to spike to unsafe levels.
A sudden dramatic increase in pH – known as a pH shock – can greatly stress fish. At pH levels over 9, ammonia converts to toxic ammonium, putting fish at risk of ammonia poisoning.
High pH also causes the water to hold less dissolved oxygen – resulting in suffocation for fish if oxygen levels dip too low. And rapid pH flux interferes with the fish’s natural osmoregulation, causing fluid balance issues.
How much baking soda is too much? Experts recommend adding no more than 1 teaspoon baking soda per 10 gallons of pond water at a time. The exact safe amount depends on the current pH reading and the particular fish species.
Goldfish and koi are especially sensitive to pH shocks. With fish like these, it’s best to make baking soda additions gradually and carefully monitor pH.
Best Practices for Using Baking Soda Safely
To use baking soda safely and effectively in your fish pond:
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Always check the pH before adding baking soda. Only add if pH needs raising.
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Add in small doses over time, not all at once. 1 tsp per 10 gallons incrementally is a safe starting point.
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Thoroughly dissolve baking soda in pond water before adding so it mixes in evenly.
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Limit use to once per week at most, unless pH is extremely low.
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Closely monitor pH daily using a quality test kit, and discontinue use if pH creeps too high.
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Do larger water changes if pH rises over 8.4 until it stabilizes. High pH water holds less oxygen, so well-aerated water is important.
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Research the specific pH requirements of the fish species in your pond. Some species tolerate a wider range than others.
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Consider alternative pH buffers like crushed coral or specialty pond buffers if fish seem stressed by baking soda additions.
With careful use based on frequent pH testing, baking soda can be used as one tool for maintaining pond health. But other management practices are also key – like routine testing for ammonia and nitrites, water changes, and filtration system maintenance.
It’s also worth researching whether any minerals or metals naturally present in the water supply could be influencing pH. Addressing the underlying cause, when possible, is better than relying solely on baking soda for pH control.
The Consensus: Fine in Moderation, Harmful in Excess
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Baking soda can effectively raise pH and help correct acidic pond water. But it should only be used when needed, not on a continuous basis.
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Excessive baking soda will rapidly spike pH to dangerous levels, putting fish at grave risk of illness or death from pH shock.
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Start with very small amounts (1 tsp per 10 gallons), only increase if pH remains too low, and cease use if pH climbs over ideal range.
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How the fish react is more important than any recommended “safe” dosage – stop using if fish show signs of stress.
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For ponds with sensitive fish, consider alternative pH buffers like coral sand instead of baking soda.
The consensus among experts is that baking soda is safe for ponds in small doses, but harmful in excess. Know the risks, test pH frequently, and start conservatively. And when in doubt, seek advice from an experienced pond pro on the proper pH management strategy for your specific pond.
Frequently Asked Questions
1. What is the ideal pH range for fish ponds?
The optimal pH range for most backyard pond fish is 6.5-8.0. Certain species have more specific preferences, like koi preferring 7.2-7.6. The key is to maintain a stable pH within the ideal range, not bouncing up and down.
2. Is it safe to put baking soda in ponds with frogs or tadpoles?
High pH can be harmful to amphibians as well. It’s best to avoid using baking soda in ponds with frogs or tadpoles unless the pH is extremely low. Even then, use sparingly because they are sensitive. Test pH frequently and do water changes to dilute if pH creeps above neutral 7.0.
3. Can I use baking soda to lower my pond’s pH?
No, baking soda does not lower pH – it only raises it. To lower pH, chemicals like muriatic acid or sodium bisulfate are needed – but these also carry risks and must be used cautiously. It’s best to address the underlying cause of low pH rather than attempting to alter pH with additives.
4. How often should I test the pH when using baking soda?
Ideally, test pH daily when using baking soda until you better understand its impact in your pond. Then at a minimum, test pH 2-3 times per week. More frequent testing lets you catch harmful fluctuations faster before fish are negatively impacted.
5. Should I stop using baking soda in the winter?
It’s generally best to stop using baking soda in cold weather when fish become less active and their metabolism slows. Colder temperatures allow more dissolved oxygen which can already cause pH to rise. Test pH before adding baking soda in winter and use reduced amounts if needed.
Tucker, Final pH values of pond waters, Table 1
| Initial Alkalinity (mg/l as CaCO3) | Amount of Sodium Bicabonate Added (mg/l) 25 | Amount of Sodium Bicabonate Added (mg/l) 50 | Amount of Sodium Bicabonate Added (mg/l) 100 |
|---|---|---|---|
| 50 | 9.9 | 9.8 | 9.6 |
| 100 | 9.9 | 9.9 | 9.7 |
| 200 | 9.9 | 9.9 | 9.8 |
A fairly large amount of chemical is needed to lower pH levels significantly, and using sodium bicarbonate does not stop pH levels from rising again. So, sodium bicarbonate is not only not very good for treating high pH in an emergency, but it is also not a good long-term solution.
Chemicals produced by some blue-green algae can give pond-raised fish and shrimp undesirable earthy flavors. Farmers sometimes attempt to remove the taint by adding sodium bicarbonate to pond water. This is the strangest way that sodium bicarbonate is used, since there is no chemical or biological evidence to support the claim that it gets rid of or stops fish or shrimp from going bad before they are harvested.
This misunderstanding might have something to do with the fact that many people put an open package of baking soda in their fridges to get rid of food smells. Sodium bicarbonate does, in fact, remove airborne odors caused by acidic or basic compounds. Certain smells in fridges are often caused by lactic acid from spoiled milk or acetic acid from things like vinegar in pickles.
When these acidic molecules in the air hit baking soda inside a fridge, they react with bicarbonate and change into compounds that don’t smell as bad. Similarly, odorous basic gases such as ammonia are neutralized to less odorous compounds when they contact baking soda.
The major off-flavors in pond-raised catfish are caused by geosmin and 2-methylisoborneol. Both compounds are cyclic alcohols produced by algae. They are neither acidic nor basic, and do not react with bicarbonate.
(Editor’s Note: This article was originally published in the July/August 2008 print edition of the Global Aquaculture Advocate.)
Common mistakes: attempts to remove carbon dioxide, lower pH, counter off-flavors
Sodium bicarbonate is one of the most common chemicals used in industry around the world. It is also known as bicarbonate of soda and baking soda. It may be the most well-known “pure” chemical compound to people who aren’t scientists, second only to sodium chloride (table salt).
People often use sodium bicarbonate to leaven baked goods, clean, deodorize, make toothpaste, and treat heartburn with an antacid. Some uses, like in toothpaste, depend on the compound’s gentle abrasive properties. But sodium bicarbonate is mostly useful because it can neutralize either acids or bases.
Sodium bicarbonate also has important uses in aquaculture. The chemical is necessary in recirculating aquaculture systems because it is added on a regular basis to restore the alkalinity that was lost when nitrification took place. Without routine bicarbonate addition, system pH eventually drops to lethal levels.
Sodium bicarbonate is also a key component of some “transport tank aids. When fish are being moved in small spaces, adding sodium bicarbonate to the water helps them keep their internal salt balance and the bicarbonate helps balance the pH of the transport water.
Besides these legal uses, sodium bicarbonate can also be abused in aquaculture. This might happen because the chemical bases for the intended uses are not fully understood. Three common misuses are attempts to remove carbon dioxide, reduce high pH and counter off-flavors.
Carbon dioxide, the end product of respiration, accumulates naturally in ponds as part of the daily photosynthesis-respiration cycle. Usually, carbon dioxide levels drop during the day and rise at night. They are highest near dawn, when dissolved oxygen levels are lowest. After phytoplankton dies off, concentrations can get very high because a lot of carbon dioxide is released when dead plants break down.
Carbon dioxide interferes with oxygen use by fish. If carbon dioxide concentrations are high, fish can suffocate at dissolved oxygen concentrations that are normally tolerated. When there is a lot of carbon dioxide in the air and not enough dissolved oxygen, fish farmers sometimes try to calm the fish down by taking away some of the carbon dioxide. Sodium bicarbonate is often used for this purpose, and large amounts of the chemical are often added to the currents that aerators create.
The origin of this practice is a mystery because it has no chemical basis. Adding sodium bicarbonate to water that already has carbon dioxide in it raises the pH a little but doesn’t get rid of any of the carbon dioxide. Strong bases, like carbonates or hydroxides, can be added to water to get rid of carbon dioxide. These bases react with carbon dioxide to make bicarbonate. Hydrated lime (calcium hydroxide) is the most common base used to get rid of carbon dioxide, but a lot of it is needed when the carbon dioxide level is high.
Rapid photosynthesis by phytoplankton or underwater plants removes carbon dioxide from water and causes the pH to rise. On warm, sunny days, pH can rise very high in ponds with plants or algae that grow quickly. This can be stressful for animals that live in the water. There are no precise guidelines for high pH tolerance, but pH values above 9. 5 are considered undesirable.
High afternoon pH seems to be most of a problem in ponds used to raise fry and freshwater prawns. This is because the fertilization methods used to get these ponds ready for stocking are meant to encourage phytoplankton blooms that grow quickly. High pH levels in the afternoon usually go down a few weeks after organic matter starts to build up in the ponds. Carbon dioxide is produced as organic matter decomposes, which reduces peak pH values.
Adding sodium bicarbonate is often suggested as a way to deal with high pH levels when it is not possible or convenient to wait for pH levels to level off naturally in ponds before adding fish. Figure 1 shows how bicarbonate changes the pH of water with different starting total alkalinities at pH 10. Sodium bicarbonate treatment reduces high pH values, and the results are almost immediate. But the results aren’t great, even when a lot of sodium bicarbonate is added to water that was already low in total alkalinity.