How to Reduce the Alkalinity of Aquarium Water

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If your freshwater aquarium alkalinity is too high, some of the dissolved minerals have to be removed. One option is to remove them by running tap water through a reverse-osmosis filter. Or, rather than removing minerals until you have the right pH, you could start with naturally soft water and gradually raise the alkalinity until it reaches the right level.

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Some fish require low alkalinity.
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Although alkalinity is often used as a synonym for "basic," the term properly refers to the buffering capacity of water. As several popular aquarium fish, such as South American cichlids, require low alkaline aquarium water to thrive, it is important to know how to reduce your tank's alkalinity when necessary in order to take proper care of your fish and keep them in optimal health. Understanding the basics of pH and water hardness can help you when you're adjusting your aquarium water.

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Alkaline aquarium water

The pH, alkalinity, and relative hardness of the water are all interrelated. Proper pH levels allow the chemical reactions taking place in the water to proceed as they should. If your freshwater aquarium alkalinity is too high or too low, it impairs these processes. The relative hardness of the water refers to the dissolved minerals in the water. These dissolved minerals, including carbonate, bicarbonate, and borate, prevent drastic changes, or buffer, the water's pH. The water's capacity for resisting pH change is called its alkalinity.

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Stabilize your aquarium's pH

While slightly lowering the pH of the aquarium water is a relatively simple process, it is difficult to drop the pH drastically or maintain low pH values without suitably low alkalinity. Even if you are able to lower the pH, the results will only be temporary, as the buffering capacity of the water will cause the pH to rebound quickly, causing dangerous pH fluctuations. To lower the high alkalinity in a fish tank enough to keep your cichlids or angelfish happy, you must first reduce the hardness, and provide them with low alkaline aquarium water.

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Get a reverse-osmosis filter

The most effective way to remove dissolved minerals from an aquarium's water is by using a reverse osmosis filter. Reverse osmosis filters force water through a semipermeable membrane that traps and removes solids from the water. In addition to removing dissolved minerals from water and reducing the high alkalinity in a fish tank, reverse osmosis filters remove some toxic substances, including chlorine, phosphate, and heavy metals. If your freshwater aquarium alkalinity is too high, this is a simple solution.

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Monitor the water's alkalinity

Be careful that you do not allow the pH to fall too low after reducing the alkalinity. With a reduced capacity for buffering acids and bases, the tank will now be more susceptible to fluctuating pH levels. Shell-based substrates, biological processes, and tannins that leach out of any driftwood in the tank are all capable of raising or lowering the pH outside of tolerable levels. Monitor your pH levels regularly with an aquarium test kit. This will help you to catch changing pH levels quickly before the water becomes dangerous for your fish.

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Start with soft water

To avoid problems that can occur with high alkalinity in a fish tank, begin with soft, low alkaline aquarium water. The alkalinity of municipal water varies from region to region, so always test your tap water before using it to fill your aquarium. If your tap water is too hard, consider installing a reverse osmosis filter on the tap or using another source of water for your fish.

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You can purchase pretreated water from fish supply stores or you can buy distilled water from the grocery store. Otherwise, you can collect rainwater or melted snow (as long as it's clean) since they both have low mineral content. Then you need to increase the alkalinity. To do this, you can add baking soda or harder water until it's the right level for your species of fish.

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