What Causes pH to Rising in Aquarium

You have to agree that as an aquarium owner, nothing breaks your heart more than seeing your fish suffer. It gets worse when they die.

One of the best ways to prevent such heartbreaking events from happening is to monitor the water in the tank, and ensure the pH stays at acceptable levels.

Unfortunately, pH levels can be a pain in the butt. Those things rise and fall more frequently than the stock market. High pH is perhaps the most common and dangerous type of pH imbalance.

If you ever want to get a handle on it, you need to understand what causes pH to rise in aquarium. For instance, some of the “harmless” rocks you added to your aquarium can increase pH and kill off your fish!

This article will provide all you need to detect and control the rise of pH in your aquarium. You’ll learn simple ways to stop the pH level from rising high enough to harm your fish.

Got questions about pH in aquariums that you’ve never found answers to?

Find the correct answers here:

What Causes pH to Rise in Aquariums?

Aquatic Plants

Some aquatic plants in your tank trap carbon dioxide and other materials which include nitrates. They act as agents that increase alkalinity, thereby increasing the pH levels. A good way to spot this is to check for excess slime and algae on the decorations, rocks, and glass of your aquarium.

Bad Filters

A damaged filter or one that isn’t working effectively will not keep leftover food and other organic material away from the water. These materials could end up increasing the pH level in the water especially after extended periods.

Rocks and Stones

Some stones in the aquarium contribute to raising the pH levels. In particular, calcium-rich rocks like limestone dissolve and mix in the water, thereby increasing the pH levels. If you added crushed stones or shells to your aquarium, chances are they’re contributing to its pH level increase.

Aerating the Tank

Tank aeration like many other activities that alter the carbon dioxide levels in an aquarium is part of what causes pH to rise in aquarium. If you expose your tank and aerate it, carbon dioxide will escape which means less acidity in the water and an increase in the pH level.

Why is a High or Low pH Level Important? What are the Effects?

You need to regulate the pH in the same way you would use a heater to maintain the water temperature in your aquarium. The reason for doing so is also the same: fish preferences. A pH level for one fish species may not be suitable for another species.

Here’s the deal:

Certain fishes have been selectively engineered to the point that their natural counterparts have different tastes. It can be fatal for your fish if the pH levels in your tank are not suitable. A low pH will burn their skin. Any form of bad pH is harmful and can contribute to health issues. 

How Do I Know the pH Level of My Aquarium?

You don’t have to do any complex calculations. You simply have to test the aquarium with a testing kit.

Most pet stores can sell testing kits but if you don’t find any, look around online. Depending on the brand and type, their prices may differ significantly, but generally, they are quite cheap.

Some stores will test your water on your behalf for free if you don’t want to spend money to buy a kit for yourself. However, you must place your water in a sample and then take it to the store. This takes time and makes it difficult to test your water every week. It’s not a long-term solution. 

Manual or Digital pH Testers

Digital pH testers are the easiest to use but are more expensive than the manual methods. It’s as easy as dipping one end into the water and the pH value will appear on the digital monitor.

Manual testing kits are more widely used and much cheaper. You will need to buy test strips made from dyed litmus paper. Once you dip these in water, they will change color depending on the pH level. To evaluate the pH, compare this color with the given color-coded map. 

Most test strips can check several parameters in one dip. These parameters include:

  • Carbonates level
  • Nitrates level
  • Water hardness
  • Nitrites level

Some manual test kits demand that you blend a sample of your water into a color-changing chemical solution, which is a little less convenient. 

You’ll have to buy more until you run out of strips or chemical solutions. Unless it malfunctions, a digital tester can operate indefinitely. Each method is effective, and the one you choose is likely to rely on how much you’re willing to spend.

What Is the Most Ideal pH Level for My Aquarium?

A pH level rise might be a good thing so your knowledge of what causes pH to rise in aquarium could also be of interest if you want to increase your pH level.

You might be wondering: How do I know if my aquarium needs a higher or lower pH?

Your tank’s pH will depend on the species of fish you keep. Your job is to recreate their natural habitat as best as you can when designing their perfect aquarium. This includes making sure the pH level is consistent with their natural environment.

If you are unsure, it’s easy to find out about the preferences of your fish. You can find it in regular fishkeeping books, or you might want to ask the staff in pet stores. 

You will note that there appears to be a different pH for each type of fish tank. Tropical tanks are typically between 6 and 7.5, while marine tanks are about 7.5 to 8.5, with the higher end of this range being reef tanks.

What’s the bottom line?

There are several exceptions to this, which is why it is always safest to abide by your fish’s unique needs. Remember to verify that your pH is sufficient for other organisms such as plants or invertebrates present in your aquarium.

How Can I Reduce The pH Level in my Aquarium?

You know what causes pH to rise in aquarium and now you want to reduce it. Here’s what you need to do:

We suggest only natural methods to reduce the pH levels in your tank if it rises above what it requires. Store-bought chemicals work effectively to reduce your pH levels but they could put your fish under stress and cause them to fall sick.

Cappata Leaves

These brown colored leaves are also called Indian Almond and they can alter the conditions of water in an aquarium. After you place them in water, they decompose and produce tannins in the process.

These tannins will lower the pH levels of your tank. They also have antibacterial properties that could help your fish if they have fin rot.

An alternative to putting the leaves in the tank is to soak them in a bucket or somewhere else. Next, pour the stained water into your tank when you change the water. This will also help reduce the effects of color change.

Peat Moss

Peat moss is a great and natural way to reduce your water pH value. It works by filtering out the contaminants and since they are part of what causes pH to rise in aquarium, removing them will lower the pH.

Simply dipping it in your tank and removing it will not have any effect. It must stay in your tank before you start to see changes in the pH level. You can make sure it stays in your water by putting chunks or pellets of the peat moss in your water filter.

The working system of peat moss is easy. Peat moss will discharge tannic and gallic acids into your aquarium, which will attack the bicarbonates in the water, decreasing its hardness and pH.

There is no definite answer to how long you have to keep the peat moss in water. It depends on your source and quality. So it’s best to start with a small quantity and keep measuring your pH until it reaches the desired level.

There’s only one catch with using Peat Moss to lower your pH level: It could discolor the water in the aquarium. You can reduce the yellow coloration by pre-treating it in a separate bucket for a couple of days before putting it in your tank.

Reverse Osmosis

In this process, you use a device to purify the water in the tank by passing through a semipermeable membrane. This allows only small molecules to pass through thereby leaving out the impurities in the water which includes any pesticides or heavy metals.

The purification method keeps your pH level at bay with a natural deionizing process.

Here’s the catch:

You will need to buy a reverse osmosis unit which could cost a few hundred dollars.

Other than buying the unit, you will only need to replace the filters periodically. The reverse osmosis method is a great long-term option that does not decolorize the water in your aquarium.


This is another material you can add to your aquarium to lower the pH levels of your water. Just like peat moss and cappata leaves, this also releases tannins into the water.

Before putting driftwood in your water, make sure the one you have is safe for fish as there are some meant for reptiles. This also colors the water and you can boil it with salt to reduce the effects of discoloration.

Bottom Line

Always take note of the type of fish you have in your aquarium. As we mentioned above, knowing your type of fish tank is also important.

Your manual or digital PH testers should help you find out if your pH level has strayed out of the required range.

Now that you know what causes pH to rise in aquarium, it’s also vital to note that pH levels never remain constant. You have to be proactive to keep them in check.

Avoid the use of bad filters, keep algae out of your fish tank, and watch the type of rocks you put in your aquarium.

If despite your best efforts, the pH in your aquarium gets out of hand, try out the pH reduction methods we discussed. Cappata leaves, peat moss, reverse osmosis, or driftwood will get you out of that sticky situation.

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