The right amount depends on your tank size and how far your pH has dropped

Baking soda raises pH by adding alkalinity to the water. The standard starting dose is one teaspoon per 50 gallons of water. If your tank is 20 gallons, use about one-third teaspoon. If it is 100 gallons, use two teaspoons. Dissolve the baking soda in a cup of tank water first, then pour it back in slowly over a few minutes rather than dumping it dry.

After adding baking soda, wait 24 hours before testing again. pH does not stabilize when ready, and testing too soon will give you a false reading. Most aquariums need only one dose, but some require a second process a day or two later if the pH is still too low. Never add more than one dose per day, even if the pH has not reached your target yet.

Baking soda works best when your pH has dropped only slightly — from 7.0 to 6.5, for example. If your pH is below 6.0, the problem is usually excess organic matter (dead plants, uneaten food, fish waste) breaking down in the water. Baking soda will raise the pH temporarily, but the underlying decay will pull it back down. Clean the substrate, do a partial water change, and reduce feeding before relying on baking soda alone.

Key Takeaways

  • Start with one teaspoon of baking soda per 50 gallons of water, dissolved in tank water before adding.
  • Wait a full 24 hours after dosing before testing pH again, because the water needs time to stabilize.
  • If pH is below 6.0, remove decaying matter and do a water change instead of relying only on baking soda.
  • Never add more than one dose per day, and space multiple doses at least 24 hours apart.
  • Baking soda raises pH by increasing alkalinity, so it works only if your water lacks buffering capacity.

Why baking soda raises pH

Baking soda is sodium bicarbonate, a base that neutralizes acids in the water. When fish waste and decaying organic matter break down, they release acids that lower pH. Baking soda counteracts this by adding alkalinity — the water's ability to resist pH change. A tank with low alkalinity will see pH swings; a tank with good alkalinity stays stable even when acids are present.

The catch is that baking soda only works if low pH is caused by low alkalinity. If your water naturally has very low alkalinity (soft water from rain or distilled sources), baking soda will raise pH. If your tank is heavily stocked or overfed, and organic waste is the real problem, baking soda is a temporary fix. The pH will creep back down as more waste accumulates.

How to measure and dissolve baking soda correctly

Use a kitchen teaspoon, not a measuring spoon from a science kit — they are the same size, but a kitchen spoon is what most people have. One teaspoon of baking soda weighs about 5 grams. For tanks smaller than 50 gallons, measure out a teaspoon and divide it by eye: half a teaspoon for 25 gallons, one-third for 17 gallons, one-quarter for 12 gallons.

Pour the baking soda into a cup of water from the aquarium itself — not tap water, because tap water may have chlorine or different chemistry. Stir until the powder dissolves completely. This usually takes 30 seconds to a minute. Then pour the mixture slowly into the tank near a filter intake or air stone so it mixes evenly rather than settling in one spot.

Do not add baking soda directly to the tank dry. Dry powder can create a localized pocket of very high pH that stresses fish in that area before the water mixes. Dissolving it first ensures even distribution.

Testing pH before and after dosing

Test your pH before adding baking soda so you know your starting point. Use a liquid test kit (the dropper kind) rather than a strip, because strips are less accurate and harder to read at the low end of the scale. Write down the number: if it is 6.2, your target might be 6.8 or 7.0 depending on what fish you keep.

After dosing, wait 24 hours. During this time, the baking soda continues to work and the water chemistry settles. Testing after 2 or 3 hours will show a higher pH than the water will actually maintain, leading you to overdose. A full day gives you an honest reading and tells you whether you need a second dose.

If pH is still below your target after 24 hours, add another dose using the same calculation. Space doses at least 24 hours apart. If you need more than two doses, or if pH keeps dropping between doses, the problem is not low alkalinity — it is excess waste. Clean the tank and reduce feeding before adding more baking soda.

When baking soda is not the right solution

Baking soda works for tanks with low alkalinity and slightly low pH. It does not work well for tanks with very soft water (near zero alkalinity), because the pH will swing wildly even after dosing. In those cases, a buffer product designed for aquariums — such as products that raise both pH and alkalinity — is more stable than baking soda alone.

Baking soda also does not help if your pH is low because of active decay. A tank with dead plants rotting in the substrate, or one where you are overfeeding and the food is decomposing, will have pH that drops faster than baking soda can raise it. Remove the source of the acid first: pull out dead plants, vacuum the substrate, and feed less. Then use baking soda to stabilize the pH while the tank recovers.

If your pH is dropping rapidly — more than 0.5 points per day — do a 25 to 50 percent water change when ready. This removes some of the acid and buys you time to identify the real problem. Baking soda is a maintenance tool, not an emergency treatment.

Baking soda versus commercial pH buffers

Baking soda is cheap and safe for fish, but it only raises pH. Commercial aquarium buffers usually raise both pH and alkalinity at the same time, which means the pH stays stable longer. Buffers cost more per dose but require fewer applications over time.

For a one-time pH correction in a small tank, baking soda is fine. For a tank that needs pH adjustment every few weeks, a buffer product is usually more cost-effective and less work. Read the label of any commercial product to see whether it raises pH, alkalinity, or both — and follow the dosing instructions exactly, because different brands have different concentrations.

Never mix baking soda and commercial buffers in the same tank without testing first. Some combinations can cause pH to spike unpredictably. If you switch from baking soda to a buffer, wait at least 48 hours after your last baking soda dose before starting the buffer.

Common mistakes when using baking soda

The most common error is testing pH too soon after dosing. Baking soda needs time to fully dissolve and distribute, and the water needs time to stabilize. Testing after a few hours will show a higher pH than the tank will actually maintain, and you will think you need less baking soda than you actually do. Wait the full 24 hours.

The second mistake is adding baking soda without addressing the cause of low pH. If your tank is overstocked or overfed, baking soda will raise pH for a few days or weeks, then it will drop again. You will end up adding baking soda every week instead of solving the real problem. Count your fish, reduce feeding, and clean more often before relying on baking soda as a permanent fix.

The third mistake is adding too much at once. A teaspoon per 50 gallons is a safe starting point. If you add three teaspoons to a 50-gallon tank because you are impatient, pH can spike to 8.0 or higher, which stresses or kills fish. More is not faster — it is dangerous. Stick to the standard dose and wait 24 hours.

Frequently Asked Questions

Can I use baking soda in a tank with plants?

Yes. Plants actually benefit from slightly higher pH and alkalinity because they use the buffering capacity to stay healthy. Baking soda will not harm plants. If anything, raising pH from 6.0 to 6.8 often makes plants grow better because the water is more stable.

How often can I add baking soda?

Never more than once per day. Space doses at least 24 hours apart so you can test and see whether another dose is needed. If you are adding baking soda more than once a week, the problem is not low alkalinity — it is excess waste or a leak in your tank. Check for these issues before continuing to dose.

Will baking soda hurt my fish?

No. Baking soda is safe for all freshwater fish at the doses used for pH adjustment. It does not introduce toxins or change water chemistry in harmful ways. The only risk is if pH spikes too fast, which happens only if you add too much at once or test too soon and overdose thinking you need more.

What pH should my aquarium be?

Most community fish do well between 6.5 and 7.5. Goldfish and plecos prefer slightly higher pH, around 7.0 to 7.5. Tetras and other soft-water fish tolerate 6.0 to 6.8. Check the species you keep and aim for the middle of their range rather than trying to hit an exact number.

Can I use baking soda in a saltwater tank?

Saltwater tanks have their own pH and alkalinity systems that are very different from freshwater. Do not use baking soda in a saltwater or brackish tank without consulting a marine aquarium guide first. The dosing and effects are not the same.