Why Do My Fish Tanks Get High PH Levels?

Written by brenton shields
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Why Do My Fish Tanks Get High PH Levels?
Maintaining proper pH levels is an essential part of keeping an aquarium healthy. (fish tank image by Tammy Mobley from Fotolia.com)

The pH level of an aquarium's water is one of its most vital aspects. Keeping the proper pH level will also keep your fish alive and healthy, and is one of the most common causes of fish death in home aquariums. It can typically be easily adjusted using chemical buffers if it's too high or too low, but unless you track down the source, maintaining the pH will be an ongoing battle. Luckily, there are several reasons the pH may be too high or too low, many of these can be easily fixed.

What is pH?

The water's pH is a level of its acidity on a 0-14.0 scale. 7.0, the centre of the scale, is considered neutral, which is the typical pH level found in most freshwater aquariums. Anything above 7.0 is considered alkaline, while anything below is considered acidic. While most freshwater fish prefer neutral water, others, like saltwater fish, prefer alkaline water, typically above 8.0. The water's pH depends on several factors that can drastically alter the level.

Water Changes

To keep water clean and fresh, many amateur fish keepers will carelessly change the water, many times too frequently. This, however, can severely affect your aquarium water's pH. Most people who frequently change the water use water directly from their taps, which can have high pH levels. This can be prevented by changing the water less frequently or changing less at a time. Typically, you should never change more than a quarter or so of the water at any one time.


Higher salinity levels can significantly raise the pH. Obviously, in a saltwater aquarium, having a pH of around 8.3 is a necessity for most marine life. But it's not uncommon for a small amount of marine salt to be added to freshwater aquariums as well, which could potentially raise the pH level.


Substrate, which is the gravel, sand or coral that covers the bottom of the tank, can affect your pH level. Crushed coral, in particular, is a substrate commonly used in saltwater aquariums that raises the pH levels. Crushed coral should not be used in a freshwater aquarium, as it will often raise the pH beyond the desired levels, and should be replaced by gravel or sand. Other materials like calcium carbonate and dolomite chips can also cause high pH levels.

Overuse of Buffering Chemicals

Buffering chemicals, like Aquarium Pharmaceuticals' product pH UP, are designed to raise (or lower) the pH accordingly, typically in a very short amount of time. If you attempt to use one of these products, it's easy to overdose, which can cause a substantial increase in the pH level. It's important to only use pH buffers as a temporary solution to alter the pH while you look for a more permanent solution.

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