The Importance Of Your Fish Tank pH Level

​​The fish tank pH level is one of the most vital components for keeping healthy fish. pH that is too low or high causes stress and illness.

Whether your fish needs low (acidic) or high (alkaline) pH depends on its species. Most freshwater tropical fish need acidic water, or water with a lower pH. Cichlids and saltwater fish need alkaline water, or water with a higher pH.

Low pH usually occurs because of overcrowding, overfeeding, or improper cleaning.

Fish living in a fish tank with a low pH may exhibit any of these six symptoms:

• Labored breathing
• Lethargy
• Decreased appetite
• Discoloration
• Infection
• Erratic swimming & rubbing

High pH in a fish tank is usually caused by using source water that has a naturally high pH. Your pH may also be too high if you have too many algae or plants. Choosing pH-altering substrate or rocks for your aquarium decor can cause high pH. The symptoms of high pH are generally the same as those of low pH.

To keep your fish healthy, you should be proactive and frequently measure the pH in the tank. Measuring the pH of your water is cheap and easy; you can buy accurate test kits at your local pet store. For difficult fish, consider buying a pricier pH monitoring unit.

Whether you should alter the pH in your aquarium depends on the health of your fish. It also depends on how far outside the acceptable range the pH is.

To lower the pH in your aquarium, use any of these five methods:

• Water changes
• Peat moss
• Driftwood
• Live plants
• Chemical buffers

To raise the pH in your aquarium, use any of these four methods:

• pH altering rocks & substrate
• Airstone
• Baking soda
• Chemical buffers

What Is pH In A Fish Tank?

pH stands for “potential hydrogen,” and it measures how acidic or alkaline water is. We measure the amount of pH in the water on a scale of 0-14. A pH of 7.0 is neutral. A pH above 7.0 (>7.0) is alkaline, while a pH below 7.0 (<7.0) is alkaline (basic).

H2O (water) contains hydrogen and oxygen atoms. Neutral water has a pH of 7.0 because it has an even number of hydrogen and hydroxide ions. pH changes because of the dissolved minerals and chemicals in the water. Whether water is acidic or basic depends on the amount and type of dissolved substances in the water.

Why Is pH Important For Fish?

pH is one of the most important components in your fish tank because it determines the health of your fish. Every species has its ideal pH level, and you need to adjust your aquarium water to suit their needs.

Fish tank water above or below your fish’s requirements leads to health problems. pH that is significantly outside their preferred range eventually causes death.

pH is also essential for breeding, as fish only spawn when the water is within a specific pH range.

What Should The pH Level Be In A Fish Tank?

The correct level of pH in your aquarium depends on the species of fish you’re keeping. Freshwater tropical fish need a more neutral pH. Freshwater cichlids and saltwater fish like more basic water.

Your freshwater aquarium pH should generally be between 6.0 and 7.5, but that will vary by species.

pH for tropical fish coming from the Rio Negro in Brazil like very acidic water, sometimes 5.5 or lower.

Your cichlid pH level usually needs to be above 8.0.

Your saltwater pH level usually needs to be above 8.0.

Fish Tank pH Level Chart

Consult this chart for your fish’s preferred pH:

What Causes Low pH In A Fish Tank?

The most common cause of low pH in a fish tank is too much waste in the tank.

Excess waste comes from:

• An overcrowded tank
• Overfeeding
• Improper and/or infrequent cleanings
• Decaying fish in the water

The pH may also be too low because of the water you’re using to perform water changes. Municipal tap and well water can be unreliable for filling a fish tank. Before using tap water to fill or top off your aquarium, you should always test it.

Sick fish in the tank can also alter the pH; move ill fish to a quarantine tank as soon as possible.

Symptoms Of Low pH In A Fish Tank

pH that’s too low will make your fish sick. Here are some signs to look out for:

• Sudden changes in appearance behavior
• Labored breathing
• Rapid gill fluttering

You’ll also notice changes in your aquarium’s environment:

• Algae growth
• Sludge or dirt on the substrate

Algae Growth

Algae growth is often one of the first signs the pH in your water is too. Algae thrives in slightly acidic water.

Excess nutrients in the water fuel algae growth, often caused by a dirty tank. Excessive light also causes it. So, overactive algae growth isn’t always a cause of low pH, but low pH can exacerbate it.

Excess algae growth is almost always a sign that the water conditions are unhealthy. Your fish will likely become sick if you don’t take care of the problem.

Sludge Covering The Substrate

Sludge or waste covering the substrate indicates that your tank needs cleaning. A dirty tank is detrimental to fish, causing a spike in ammonia, nitrites, and nitrates. Excess waste also causes a change in the pH, which makes it even more likely your fish will become ill.

Sludge often occurs due to overfeeding. The food sinks to the bottom of the tank and settles on the substrate where there’s little oxygen.

To prevent a build-up of waste, only feed your fish as much as they can eat in about three minutes. Use a net to remove any leftover food after those three minutes are up. You’ll also need to keep on top of tank cleanings; perform 25% water changes every one to two weeks.

Labored Breathing

Labored breathing shows that something is wrong: fix the problem immediately. Acidic water makes it difficult for fish to absorb oxygen through their gills. Fish can’t survive for long if they’re laboring to breathe, so you must correct the pH levels immediately.

Fish struggling to breathe may spend much time at the bottom of the tank. They may also spend a lot of time at the tank’s surface gasping for air. You’ll notice their gills moving more rapidly as they struggle to take in water and oxygen.

Lethargy

Fish dealing with low pH conditions become stressed and have difficulty swimming. They’ll become less active than usual and swim sluggishly around their tank. You may also notice them resting more on the substrate at the aquarium’s bottom.

Decreased Appetite

Stressed, sick fish are less likely to eat, so you’ll see them consuming less food than usual. They may refuse to eat entirely.

Discoloration

The happier a fish is, the more vibrant its colors will be. A sick or stressed fish loses color and appears much paler than usual.

Infection

Fish living in acidic conditions have lowered immunity. They are more likely to fall ill and develop infections like ich. Ich is a parasitic infection that occurs on the body in white spots. Initially, you may only see a few spots here and there. As the infection spreads, the spots may cover the entire body.

Your fish may also develop fungal infections. They appear as fuzzy white patches on the body, often on the mouth or gills. Bacterial or viral infections usually appear as red spots.

Erratic Swimming & Rubbing

Acidic water can be painful and irritating to your fish’s skin, so they seek ways to relieve the irritation. They may swim erratically around the tank in short bursts. They may also begin scratching themselves against the side of the tank or on decorations. Such behavior often indicates that your fish has also developed an infection.

What Causes High pH In A Fish Tank?

Low pH is more common than high pH, but either can be as detrimental as the other.

pH that is too high is most often a result of your source water. It’s important to always test your source water before adding it to your tank, so you know which pH you’re starting with. Once you know the pH of your source water, you can adjust it up or down accordingly.

Too many algae or plants can also cause high pH in the tank. Algae and plants survive through photosynthesis and respiration. They create oxygen during the day when exposed to light and release carbon dioxide at night.

Plants produce oxygen by depleting the carbon dioxide in the water. Having lots of plants or algae may decrease the carbon dioxide too much. A decrease in carbon dioxide must be met with an increase in carbonate alkalinity. Otherwise, you get high pH.

Your high pH may also result from specific substrates and rocks. Some of these materials are explicitly meant to raise pH. Aquarists who own cichlids or saltwater fish often find them helpful.

For tropical freshwater fish, they can be a problem. Less experienced aquarium keepers may choose these items for their aesthetics. It’s not always clear that they alter pH.

Symptoms Of High pH in A Fish Tank

Fish living in overly basic water experience many of the same symptoms as those in acidic water:

• Excess algae growth
• Lethargy
• Labored breathing
• Bacterial, viral, parasitic, or fungal infections
• Erratic swimming & rubbing

How To Monitor pH In A Fish Tank

You’ll need to watch the pH levels in your aquarium to keep them safe for your fish. I recommend testing your pH once every two weeks or at least once a month. Keep a logbook to monitor trends and notice potential problems before they arise.

You should also check your pH levels anytime a fish becomes ill or dies. You also need to check it the day you begin using any medications. Check it again on the final day of medicating, and a week after the medication has stopped.

Allow The CO2 To Dissipate

Experts say you shouldn’t test aquarium water straight from the tank. The CO2 (Carbon dioxide) inside the tank can skew the results, making the pH appear lower than it is. Instead, remove some water from the aquarium and keep it in a container for a couple of days. Use an airstone to aerate the water to get rid of the CO2. After a couple of days, you can test your water.

The Best Option — Liquid Test Kits

For most aquarium hobbyists, the best way to test your pH is to use a liquid test kit. You’ll take a sample of your aquarium water and place it in a test tube. Then, you add a few drops of solution from a bottle into the test tube and shake it. After a few seconds, the water changes color to show your pH levels.

I prefer the API Master Test Kit. It gives you the tools to measure your water’s pH, ammonia, nitrites, and nitrates. It is an affordable option that is more accurate than test strips.

Least Accurate — Test Strips

Test strips work similarly to liquid test kits, but you simply dip a strip of litmus paper into the water. After a few moments, the paper will change colors to present your results. Test strips are the least accurate way of testing your water. They are the cheapest option, however.

Most Precise — pH Meters

The most precise way to test your pH levels is by using a pH probe that attaches to a pH meter. You’ll need to calibrate your probe before each use. Then, you’ll simply dip the probe into the water, and it’ll provide your reading. pH probes are usually only used by aquarists taking care of extra sensitive fish. They are more expensive than liquid test kits.

Altering pH

Strive to set up your aquarium with the proper pH before purchasing and adding your fish. Some hobbyists don’t realize pH’s importance until they’ve bought their fish.

The pH doesn’t necessarily need to be perfect. pH levels close to your fish’s preferred range, but slightly outside it, are probably okay. Fish that aren’t showing signs of sickness or distress probably aren’t minding that the pH is slightly off.

Fish that are showing signs of distress and illness need their pH corrected. Make corrections slowly and avoid rapid fluctuations.

How To Lower pH In Aquarium

There are ways to adjust the pH level in your water to suit your fish’s preference.

Water Changes

The best way to lower the pH in your aquarium is by performing water changes. Remember that doing so only works if your source water has a pH lower than your tank’s. The same goes for performing water changes to raise your pH. RO (reverse osmosis) water is excellent for lowering the pH in your aquarium.

Peat Moss

Peat moss is ideal for lowering pH and adds a natural look to your aquarium. You can mix peat moss into the substrate, weave it into decorations, or glue it onto rocks. You can also keep the moss in a mesh bag if you prefer not to see it or deal with it floating around your tank.

Driftwood

Driftwood is another natural buffer that also acts as a decoration. Driftwood also provides plecos and bottom feeders something to suck on. It is a good place for fish to hide while simultaneously lowering pH.

The downside to driftwood is that it turns your tank water light to dark brown. Driftwood contains tannins that decrease pH and cause the color change of your water. You can boil your driftwood to remove the tannins before adding the driftwood to your tank. Boiled driftwood no longer contains tannins and won’t act as a pH buffer.

Live Plants

You can never go wrong with live plants. They increase CO2 levels at night to lower pH and increase oxygen levels during the day. Fish tanks containing live plants have healthier water and healthier fish. Live plants also add to the aesthetic of your tank.

Chemical Buffers

One of the easiest ways to alter the pH in your aquarium is by using chemical buffers. Like baking soda, you’ll mix the buffer and the water in a separate bucket. Test it before introducing it to your tank. Be cautious of how much you use because artificial buffers can rapidly raise or lower the pH.

Some aquarists prefer not to use chemicals in their tanks. Still, they are effective, and pH buffers don’t seem to affect fish negatively.

Chemical buffers aren’t a permanent option; you’ll need to add more to the water with each water change.

How To Raise pH in Aquarium

Saltwater fish and cichlids need a higher pH than tropical freshwater fish. So, you’ll need to know how to raise your pH. You’ll also need to track the pH and learn how to increase it if it drops too low.

pH Altering Rocks & Substrate

The most natural way to raise your pH is to add pH-altering rocks and substrate to your tank. Rocks that raise pH include limestone and marble.

The calcium in the stones releases slowly so the water can maintain the new pH levels for an extended time. The slow release of the rock’s calcium also prevents the pH from changing too drastically.

Crushed coral substrate is an excellent option for saltwater fish. Limestone is suitable for any fish needing a higher pH.

You can also add shells as a natural decoration and a way to increase your pH. Be careful to disinfect any shells you pick up from the beach thoroughly. It’s safer but less cost-effective to buy shells from the pet store.

Add An Airstone

Increasing the aeration in your tank decreases CO2 (carbon dioxide) and increases pH. Before adding more aeration to your tank, be aware of how much flow your fish like. Fish that prefer calm water become stressed if you add too much flow to their tank.

Baking Soda

Adding baking soda to your tank is another natural way of increasing the pH. Be careful not to use too much — you can always add more later if needed. Never add baking soda directly to your tank. Mix baking soda and water in a separate bucket and test the water before introducing it to your tank.

Chemical Buffers

You can use chemical buffers to raise your pH just as you can lower it.

FAQs

About Kaylee Keech

Kaylee has a large goldfish tank filled with feeders she 'rescued' from her old job at the pet store. She also has two small, freshwater community tanks. Her favorite fish became the seahorse after she cared for one during her marine biology course. It's one of her dreams to set up a seahorse tank in her home.