What’s so important about the pH levels in your freshwater aquarium? Why is a common water quality issue like low pH not suitable for some species of fish in your marine tank?
Well, if the pH levels in your fish tank are unstable or not suitable for the fish species you keep, your fish could get seriously sick or even die.
In this guide, we answer many of the questions that hobbyists ask about water pH in their aquariums. Also, we explain how you can raise the pH when you need to.
What Is pH?
Basically, pH depends on several factors, including:
- Chemical concentrations
- The type of substrate you have in your setup
- The presence of trace minerals
The pH Scale
The pH of water is measured using a scale that ranges from 0 to 14. According to the scale, a pH of 7.0 is neutral. Anything below that number means that conditions are more acidic, or you have “soft water”, and at levels above 7.0 you have alkaline water, or basic water, as it is sometimes called.
All aquatic creatures, including fish, are tolerant of different pH levels, influenced by what’s in the fish’s natural habitat. That means that while high alkalinity levels are acceptable for one type of fish, those levels might be bad news for another. Hence the need for you to thoroughly research every fish species’ requirements before adding it to your setup.
Suppose the pH levels of the water in the aquarium are not suitable for your fish. In that case, the fish will likely be stressed, become sick, and potentially even die.
How pH Levels Can Affect Water Chemistry
The water pH can impact several other elements of water quality and chemistry in your setup.
If the pH drops below 6.0, the bacteria responsible for getting rid of ammonia, nitrites, and other toxic elements from the water begin to die off. An ammonia spike will most likely result, potentially leading to fish death and an aquarium without fish. To make matters even worse, the water pH heavily influences the toxicity of that ammonia.
pH And Ammonia
The ammonia in your fish tank water is created by combining ammonia, NH3, and ammonium ions, NH4+.
The pH heavily influences the concentrations of both of those ammonium compounds. So, in water where the pH is above 7.0, conditions are alkaline and more ammonia is present. When the pH is below 7.0, you have acidic water and there are more ammonium ions. Of those two compounds, it’s ammonia that’s most dangerous to your fish.
So, if you accidentally raise the pH, you’re making the water more toxic for your fish. For that reason, you should never tinker with the pH while you’re cycling a new tank. Once the tank has finished cycling, there should be no ammonia present in the water, making it safe to adjust the pH.
What’s The pH Of Tap Water?
Most aquarium fish keepers use tap water to top up their aquariums. Of course, tap water has a pH value, and that can vary, depending on where you live. So, how do you find out the pH of your domestic water supply?
To find the true pH of tap water …
- Run a tap water sample into a bucket, and oxygenate the water with an air stone.
- Allow the bucket to “rest” for at least 24 hours.
- Now, you can test the pH. Take a note of the reading.
- Wait a further 24 hours, and then retest the water. The pH reading you get is the correct one for your tap water.
You must allow the water to “rest” for 24 to 48 hours because the content of carbon dioxide in the water causes the pH level to drop. If you agitate the water surface using an air stone, you pull oxygen from the air into the water, simultaneously driving excess carbon dioxide from the water into the air.
The decline in carbon dioxide levels in the water pushes up the pH level. So, the pH level you get after “resting” the water will be the true one. That’s because the oxygen and carbon dioxide exchange in your aquarium is a constant process. Of course, if you have any decorations or chemicals in your tank, they could also influence the pH.
What’s The Relationship Between pH And kH?
Another critical element of the water chemistry in your fish tank is the kH level.
kH refers to the concentration of carbonate and bicarbonate ions in the water. kH is also a good barometer of the water’s ability to buffer or neutralize acids without drastically changing the pH. So, the higher the kH level in the tank, the more stable the pH should be. If the kH is too low, the pH value is more likely to vary dramatically.
Consequently, if the kH is under 4.5odH, observe your tank water for significant swings. You must conduct water changes regularly, as the kH will drop over time. So, performing frequent (weekly) water changes is the best way to keep the pH stable and within suitable parameters.
What’s A Suitable Aquarium pH Level?
A pH of 7.0 is considered neutral. Most fish and freshwater tropical critters need a pH that’s between 6.8 and 7.6, depending on the type of fish tank you have. However, I would urge you to research the species you want to keep to make sure that they all have the same pH tolerance.
Use An Aquarium Water Test Kit
The best way to check the water chemistry in your aquarium is to use a reliable aquarium water testing kit available at all aquarium shops.
You can get Aquarium test kits in dip strips or solution form, but they both work in the same way. Basically, you compare a sample of your tank water with an included color chart.
The water’s color equates to the pH or kH level indicated on the color chart. Unfortunately, these kits can be inaccurate, and you can end up with a false reading.
Also, kits have a typical shelf life of around six months. If you have a test kit that’s older than that, the results might be inaccurate.
As a rule of thumb, it’s best to perform two tests, following the instructions very carefully. Alternatively, your local fish store will test your tank water for you, usually free of charge.
How To Raise pH Levels In Your Aquarium
As previously mentioned, a severe drop in pH can cause serious problems for your fish. However, there are many adjustment methods to correct the problem.
Increasing the amount of dissolved oxygen in the water is an effective method to increase your pH level. It also reduces the carbon dioxide concentration. Carbon dioxide is acidic, producing carbonic acid when it’s dissolved in water. So, elevated levels of carbonic acid will significantly lower water pH.
You can oxygenate your water by:
- Site your aquarium filter outlet above the water surface. That agitates the water, aiding the movement of oxygen into the water from the air above the water.
- Use an air pump or powerhead to increase the flow within the aquarium. That also serves to move air into the water. However, make sure that your fish are tolerant of a strong current first.
- Carry out regular water changes to maintain good dissolved oxygen levels and decrease the concentration of carbon dioxide.
Partial Water Changes
As pollutants like fish waste accumulate in the aquarium water, the pH can gradually drop.
Two ways you can reduce pollutants and control certain aspects of water quality in the tank are keeping your aquarium substrate clean by vacuuming it every week and not overfeeding your fish. You also need to replace around 20% of the tank water every week, replacing it with dechlorinated tap water to remove excess pollutants from the water.
Add Baking Soda
Adding a small amount of baking soda is another common method that will raise the pH in the tank water. However, you need to do it regularly to maintain the results or the pH will quickly fall back to its original level.
Add 1 teaspoon of baking soda per 5 gallons of water to elevate the pH but do so slowly so that you don’t stress your fish.
You can also buy chemicals like sodium carbonate that will elevate the pH levels in your aquarium, but, as with baking soda, you will need to reapply them regularly to keep the levels stable.
Change The Aquarium Substrate
A very effective way of raising the pH in your tank is to use a different type of gravel for substrate. The best calcium carbonate-based gravels are:
- Crushed coral (calcium carbonate gravel pieces)
- Petrified coral rock
- Certain kinds of shells
These are commonly used in African cichlid setups, which generally have a higher pH than most regular tanks. However, you must check the pH regularly after you’ve changed the substrate, as your pH could end up significantly higher than you intended.
If you don’t want to tear down your tank completely, you can place the materials in your filter unit instead.
A combination of driftwood and bogwood are very common aquarium decorations that can leach tannins and tannic acid into the water, as in a blackwater biotope, which causes the pH to drop.
You can solve that problem by replacing natural wood with resin decorations that look like wood. However, if you want to keep the wood, you could try soaking it in water or boiling it to get rid of the tannins. Note that peat moss also releases tannins.
To keep your aquarium fish happy, healthy, and thriving, you must have the correct pH levels in your tank for the beautiful fish species that you’re keeping.
Problems with a pH that’s too low can be overcome by using one or more of the methods suggested in this guide. However, it’s important to note that the pH level must remain stable, as fluctuations in water chemistry can be fatal to some of the more sensitive aquarium fish species.
Do you have any top tips that worked to stabilize, the pH in your tank? Tell us your secrets in the comments box below!