What Causes High pH in Aquarium?

fish and coral on aquarium

If you have an aquarium, you have to take care of the chemical balance of your water. Your fish will affect the makeup of the water, so it is wise to check it and adjust it as needed.

If you have an unbalanced tank, your fish might not flourish. To avoid problems like high pH in your aquarium, learning why it increases is helpful.

When aquarium water is unbalanced, and the pH levels are off, the water will be either acid or alkaline. Levels are measured on a scale of 1 to 14 with these ranges:

  • Acid: 1-6.9
  • Neutral: 7
  • Alkaline: 7.1-14

What Causes High pH in an Aquarium?

Causes High pH in an Aquarium

So, what causes high pH in an aquarium? There are several reasons. The rocks and gravel in your tank can increase the pH level because the calcium in them dissolves into the tank.

Another reason why levels increase is due to plants in your tank. When plants absorb carbon dioxide and nitrates, pH levels increase. 

A high alkaline environment can be dangerous for aquarium fish. If there is too much alkalinity in the water, fish can develop alkalosis, and their swimming becomes excited and chaotic.

Their fins will be wide open, and you might notice mucus in them. Some types of fish might show alkalosis by swimming slowly and with labored breath. 

Your tank might also show signs of high pH. Aquariums with high pH have algae growth and slime on the plants and decorations. Most fish prefer neutral pH, deviations from it can be toxic for them. 

It is essential to understand what causes pH to increase and how to remedy it if you want to keep your fish healthy. In most cases, aquarium water pH lowers over time.

By adding small amounts of tap water, you can quickly increase the pH, but if it gets too high, you have to learn how to lower it.

What Raises pH in An Aquarium?

Raises pH in An Aquarium

Adding Tap Water to An Aquarium

One of the quickest ways to increase the pH level in a fish tank is to add tap water. The pH levels can also increase when people add new fish in their bags as the water is often from the tap.

City water systems often have high alkalinity which can change the way that water tastes. It can also build up scale in plumbing systems and coffee makers. 

Humans will not have problems drinking water with high alkalinity, but fish do. That is why tap water does not work well for them. 

Not Changing the Filter

Because fish leave waste in the aquarium, it is essential to change the filter regularly. Their excrement and other material from food and chemicals in the water can increase the pH levels. When the filter no longer functions appropriately, those waste products stay in the water, and your fish suffer. 

Pick a day each month to change the filter in your tank. If you find that the filter gets dirty before the date arrives, then change it more frequently. If you want your fish to live, then you have to take care of the tank. 

Some fish owners will also clean the tank each time that they change the filter. Most filters will not catch all of the waste products, so cleaning the tank is the only way to get rid of everything that could increase the alkalinity.

An aquarium vacuum makes it easy to get rid of leftover food and waste. 

When you change the tank filter, the water will have more carbon dioxide which lowers the pH levels. Another way to lower pH is to add vinegar, which is actually an excellent substance to use to clean the interior glass of your aquarium. 

Different Types of Tank Features

There are some tank features that lower the pH in the tank. There are also features that will increase the pH levels, too. Shells and crushed coral increase pH levels.

There are some fish that actually like high pH levels, like African cichlids. But most fish prefer neutral numbers. 

Limestone is another rock that increases pH levels. Unfortunately, many people add stones that increase pH levels without knowing what they are doing. 

Some types of chemicals will also increase pH levels. If you buy your aquarium somewhere other than a dedicated pet store, you might be using unnecessary chemicals that do more harm than good. Read the chemicals before you put them in your tank. 

No Driftwood

If you have too much pH in your aquarium, notice what is missing. Adding driftwood to your tank will begin the process of lowering the pH levels.

Along with driftwood, peat moss will quickly neutralize your aquarium. You can put driftwood at the bottom of your tank and peat moss in your substrate or filter. 

Not Enough Carbon Dioxide

CO2 lowers pH levels, too. If you have high levels of pH regularly, you might want to get a pH pump to add the necessary standards to your tank. Cleaning the filter or replacing the filter lowers pH levels by improving circulation.

What is the Best pH for an Aquarium?

Best pH for an Aquarium

In a freshwater aquarium, the best pH level is low to neutral, between 5.5 and 7.5. Saltwater fish prefer a high pH, around 8.0 or higher.

Freshwater fish do not like salty water, and saltwater fish do not like unsalted water. Unfortunately, no matter what type of fish you have, maintaining the perfect pH is not always easy to do. 

If your tap water is hard, it will raise the pH levels in your tank every time you fill it. If you have freshwater fish and hard water, put your tap water through a water filter to quickly lower the pH levels.

You should test your aquarium’s water regularly, especially after you have added tap water. 

Once you’ve tested the water, you should fix any pH problems that you find. If you wait too long to adjust the alkalinity levels, your fish might die.

When pH increases, ammonia and other harmful chemicals increase. Fish cannot adapt to pH levels that are too high.

Monitor pH Levels

Monitor pH Levels

When you buy a new tank, you should closely monitor the pH levels. You should pay close attention to your fish and their behavior as you break-in the new aquarium. Young fish often struggle when pH levels are off, and new tanks can have unexpected issues. 

It is commonplace for certain types of fish to have tight pH ranges. And, some fish will not reproduce if the pH levels are off by just a little bit. When you build a new tank and add new fish, be sure that they all need the same pH. 

There are several ways to test pH levels. You can use a pH test kit. You put water into a test tube and squirt the required number of drops of pH solution into the test tube.

The water will turn color, and you compare it to the levels on a test kit card. It usually takes a few seconds for the test tube water to change color, but these tests are accurate. 

Unless you haven’t clean the fish tank or filter recently, the pH in your fish tank should be close to the pH of your tap water.

You can test your tap water with the same test kit you used to check the water in your tank. Most fish parents will test the water twice per month. 

If you notice that the pH numbers are too high or too low, you should keep a record of the numbers. Include filter changes and tank cleanings in the log, too. This will give you the information you need to evaluate how your water changes. 

It is a good idea to check your water in two situations. The first is before you add a new fish. Test the water in the fish’s bag and tank so you can determine if you have to make any changes to the water in either place. You should also check the water if a fish dies in your aquarium to see if pH levels caused it.

Why You Can’t Mix Different Types of Fish

You wouldn’t want to put goldfish in the same tank as neon tetras. Goldfish like neutral water with a pH range of 7.0 to 7.5.

But, neon tetras prefer acidic water with a lower pH of 5.8 to 6.2. If these two types of fish share an aquarium, one will not thrive. Most pet shops keep similar fish species in the same tanks because of their preferred pH numbers. 

As an aquarium owner, you should also be aware of what your fish will do when you have to take them out of the tank.

Many fish experience trauma when moved from the water at the pet shop to the water in their new home’s fish tank. Fish can experience shock and may not survive the move.


Please enter your comment!
Please enter your name here