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Alkalinity vs pH Scale: What is the Difference?
Two concepts that are easily confused are alkalinity and pH. After all, pH is the scale of how acidic or basic (aka alkaline) the water is. Alkalinity, on the other hand, is the measure of the water’s resistance to changes in pH.
In other words, alkalinity describes the potential volatility of the pH levels: how easy or difficult it is for the pH to suddenly and materially change.
What precisely is being measured to determine alkalinity? Whereas the pH scale measures quantity of hydrogen ions, the measure of alkalinity examines the presence of alkaline compounds such as carbonates, bicarbonates and hydroxides.
Because sudden changes in pH levels can be fatal to fish, alkalinity is important to maintain at proper levels to reduce the probability of such instability.
How to Test Alkalinity of the Aquarium
You can test the alkalinity of water in a number of ways. For most freshwater aquariums, the target range is generally 3-8 dKH (degrees of carbonate hardness). In a saltwater aquarium, the dKH is a bit higher around 7-11.
One unique and preferred way is to use a digital tester, such as the Hanna Instrument HI775. Great results have been reported by using this tester, being described as easier to read and more commonly accurate than color strips. Though it is pricier than the color strips, customers generally agree that the added value is worth it. It is important to get accurate results when it comes to alkalinity.
Another way of testing is by using a test tube and adding drops of a solution, such as with the API KH Test Kit. What is KH? This stands for “Carbonate Hardness,” and it is distinct from alkalinity in that it only measures the presence of two compounds: carbonates and bicarbonates. While it leaves out other compounds that are generally included in the measure of alkalinity, it’s important to note that carbonates and bicarbonates are generally the most prevalent compounds in water which contribute toward alkalinity. Others, like hydroxide, play a more minor role. This KH test kit has been included here for its overall positive reviews, especially of its accuracy.
If you want a more comprehensive water test that includes both alkalinity and KH, along with total hardness (GH), nitrate, nitrite, chlorine and pH, you should check out this color card test: SaySummer 7 in 1 Aquarium Test Strips. When using this method for the first time, it might be beneficial to cross reference it with another test if available. There have been a few comments that the color is difficult to read, and sometimes it has presented bad measurements. As far as such kits generally go, however, this one has been highly rated by most customers as being accurate, quick and easy to use.
Symptoms of Low Alkalinity
When water has low alkalinity, you may find a number of concerns affecting the health of your fish.
Immunocompromised
The fish will become more susceptible to disease, because their immune systems are weakened. Signs may include pale appearance or even stunted growth.
Increased toxin levels
You may find that ammonia and nitrate levels (toxic substances) are increased, because the ability to break down toxins is hindered in a low alkaline environment. Bacteria that are beneficial to the internal balance of the environment, due to their ability to break down waste, begin to suffer under low alkaline levels.
Volatile pH levels
With high alkalinity comes high volatility of pH. Fish are harmed when pH levels move outside their adapted range, but even more so if the change happens suddenly. The more alkaline the water, the less quickly pH levels are likely to change materially.
4 Main Causes of Low Alkalinity
The first step to solve the problem of low alkalinity is to determine the root of the cause. Fish can be very fragile and will not tolerate low alkalinity in their tank; it is only a matter of time before pH levels swing with too much variation that places stress on the health of the aquarium life.
Causes of low alkalinity are generally one of the following:
Too many fish
If a tank is overcrowded, more oxygen is being consumed and more carbon dioxide is being released into the water. This carbon dioxides dissolves in water to form carbonic acid, which lowers alkalinity.
Insufficient minerals in the water
This can be caused by over-filtration or by using reverse osmosis for the entirety of the water which is added to the aquarium.
Acidic water source
It is always a good idea to test the water which is being added to the aquarium, before you add it. That way, you can determine how much acidity is present at the beginning. Hard water often serves to raise alkalinity due to its mineral content.
Use of unapproved cleaning products or tools for the aquarium
Be sure to use only aquarium-approved products when cleaning decorations, glass, substrate, etc.
How Do I Fix Low Alkalinity in my Tank?
Raising alkalinity of the water can be a relatively simple process. Here are a few ideas to consider:
Add baking soda
A favorite method among aquarists is to simply add baking soda (sodium bicarbonate) to the water. This should only be done if the fish are removed from the tank, as sudden changes can cause shock to their systems. A general rule of thumb is to add 1 teaspoon of baking soda for every five gallons of water. Making this a gradual addition over several days might be wise, so as to avoid too much change all at once. For example, if you have a 20-gallon tank, consider adding one teaspoon for four days in a row.
To read more about the process of adding baking soda, check out this article.
Change the substrate
Using a substrate that is rich in calcium carbonate is a way to gradually increase the alkalinity over time. Popular substrates for this purpose include crushed coral and aragonite sand.
Add to the substrate
In addition to the substrate, adding vermiculite can also increase alkalinity. These are not to be used as the main substrate, however, and vermiculite must be held down under the main substrate.
Use a different water source
The answer may be as simple as starting from a different point of origin. Low alkaline water can result from over-filtration or reverse osmosis methods, or simply from the more acidic source of water (soft water).
Apply a product
Consider the use of a product such as Seachem Alkaline Buffer, which should be applied in small doses (see recommended dosage) and will likely also raise the pH along with the KH of the water. It is important to make sure that there is capacity for pH to rise along with KH. Check the specific requirements of your sea life before applying this method.
Symptoms of High Alkalinity
High alkalinity can also present problems for the aquarium. A few of its effects include:
Bacterial infections
Fish naturally are protected by a layer of mucus on their skin, which is burned away with high alkalinity. This leaves them vulnerable to infections, and can even lead to deterioration of fins, skin and gills.
Respiration problems
Gill damage can result, which stresses the ability of fish to take in enough oxygen.
Beneficial bacteria suffer
When fish and plants produce waste, or when food goes uneaten, this is broken down by beneficial bacteria present in the water. High alkaline environments cause this bacteria to suffer, meaning toxic waste builds up and increases ammonia levels.
Calcium deposits
On the tank itself, you may see a buildup of calcium deposits on equipment, decorations and glass. The water may also become cloudy.
3 Main Causes of High Alkalinity
High alkalinity is often caused by one of the following:
Hard water source
First check your water source and test it separately from the aquarium. Water with a greater concentration of minerals may be the cause, and simply changing the source or mixing the source with reverse osmosis filtered water can change the balance.
Too much waste
Whether due to a neglect to clean or filter, or because of too many fish, waste can build up in the aquarium and boost alkalinity levels too high.
Mineral-rich substrate
Consider whether there is crushed coral, aragonite, peat moss, vermiculite, or any other mineral-rich substrate or decoration in the water. If so, this may be a cause of high alkaline levels.
How Do I Fix High Alkalinity in my Tank?
Add plants
Plants provide many benefits to the ecosystem of the tank, including the absorption of carbonates and bicarbonates, which are the main contributors to alkalinity.
Don’t overfeed
Monitor the eating habits of your fish, and make sure that food is not being left over in noticeable amounts. If this is happening, consider reducing the amount or frequency of feeding.
Change water frequently
Keeping the tank clean is imperative, and testing the alkalinity of the new water is important for maintaining balance. You may not want to change all of the water at once, but rather add incremental amounts of distilled or reverse osmosis water until the KH is back in the recommended territory.
Releasing tannins
Indian almond leaves, peat moss, oak leaves, driftwood and catappa leaves naturally release tannins into the water, which serves to lower alkalinity. This can cause slight discoloration to the water, so it’s best to use this method sparingly.
Vinegar and lemon juice
Adding small amounts of either vinegar or lemon juice over time can reduce alkalinity. Consider using 1 mL per gallon. This will also affect pH, so keep this in mind.
Conclusion
Maintaining the proper range of alkalinity within your aquarium water will serve to avoid many potential issues of fish health, water appearance and pH swings. It is closely related to pH, and a change in alkalinity almost always affects pH levels in one way or another. Testing alkalinity and pH regularly is crucial, especially when making changes. Now that you know what to look for in determining the source of any issues, you can make an informed decision on how to make proper adjustments to keep your underwater world both comfortable and prosperous.