Skip to main content

Is the pH in your aquarium normal? Here’s how to tell

All aquarists know that taking care of fish is tougher than it looks. Your bird, hamster, and dog breathe the same air that you do, but tank dwellers have specific needs for their environment that you have to monitor. In addition to oxygen and nutrients, you have to closely watch pH levels. If you think back to high-school chemistry, you’ll remember that pH measures how acidic or alkaline something is (like lemon versus baking soda). The ideal pH will vary depending on your fish and whether you’re looking at a saltwater or freshwater ecosystem.

Hand holding a pH testing kit next to an aquarium

How to test pH in an aquarium?

To find your pH level, you’ll need a good testing kit and you’ll want to test frequently. Before trying this out, though, check your water source. It’s helpful to know the pH of your water before it goes into your tank when you’re figuring out how to adjust it. For most tanks, you should be testing biweekly to maintain the correct levels. Keep a record of every reading and check water under the same conditions each time, meaning the same time of day and approximately the same number of hours after feeding.

You have a few different methods for analyzing your water, ranging from testing strips (least accurate) to digital testers (most accurate). With strip kits, you first draw some of the tank water into a tube. Next, you add a drop of the testing solution and wait for it to change color. Compare the water color to the color-coded strip, which will tell you the pH value of your tank. You may need more than one kit if you have different tanks with different pH requirements.

Fish swims in an aquarium
Delbert Pagayona/

What is a good pH level?

The optimum level will depend on which fish you have in your tank and what the environment is like. Generally, the pH of a freshwater tank will run a little lower than a saltwater one. For freshwater, you’re looking at anything between 6.5 and 7.5. Adjust depending on the fish you have and be mindful about putting together only species that like similar acidity levels. Some freshwater fish fall out of this range, too, like certain types of tetras, which means you’ll have to find others who can coexist in that specific range if you mix species.

For a saltwater aquarium, you want something more in the 7.6–8.4 range, but reef tanks need to stay on the higher end. If you’re growing coral, you need to pay particular attention to stabilize the pH between 8.0 and 8.4, so make sure the fish you have will thrive with the coral.

What causes high pH in an aquarium?

You may test your water when you set up your tank and find it perfect, but slowly pH starts to creep up or down. A few things can cause this, and unfortunately, some very regular processes can contribute to it. If you notice your pH level going up, it could mean you have too many plants or stones. Because plants “breathe” CO2, they can change the water quality toward alkalinity. Your rocks, too, might slowly dissolve, releasing calcium into the water. These are both common problems and easily fixed by removing some of the offending decorations, then testing again for any change. 

The symptoms of low pH in a fish tank are a little different. This usually results from fish waste that is not properly filtered out. Sometimes fixing it will be as easy as replacing your filter pieces to bring them back up to maximum ability.

How to fix your pH level?

There are some quick ways to raise or drop the level, but determining the culprit behind your pH issues will be just as important, or it will keep getting out of whack. Commercially available treatments will help easily change things up. If your pH is too low, adding a few more rocks or shells will make a difference and will keep working, rather than acting as a one-time fix. Likewise, removing these and adding driftwood or peat moss brings down your pH level.

Unfortunately, significant pH drops, or very acidic water, can kill your fish, so you need to be vigilant about testing and adjusting. Living in water not right for your fish will cause extreme stress and even burns on his skin if it’s too far outside his comfort zone. Remember, staying relatively consistent within the range is important, too. With proper testing, you’ll keep him happy in his perfect environment.

Editors' Recommendations

Rebekkah Adams
Rebekkah’s been a writer and editor for more than 10 years, both in print and digital. In addition to writing about pets…
How to tell if your guinea pig loves you – some ways may surprise you
These are the signs your guinea pig loves you as much as you love him
A happy guinea pig hangs out in the grass

We know how much we love our pets. The question is if they love us, too. It can be tricky to tell how animals feel since they can't tell us about their moods. But that doesn't mean we can't ever figure out what's in the minds of our furry friends.

Guinea pigs in particular make a lot of interesting noises and show postures that help us decipher their thoughts and feelings. By paying close attention to your little guy and learning a bit about how he thinks, you can get a pretty good sense of his inner goings-on. And you won't have to watch very long to confirm that your guinea pig loves you.

Read more
Is your fish tank for bettas too small? Here’s are the do’s and don’ts of betta care
Care tips to keep your new betta fish happy in the right size tank
A betta swims with plants in its tank

While the betta craze may have died down a little, you still see many of these beautiful blue fish in homes and in stores. It's true that they make great pets, even for a novice aquarist, since they don't require an overly extensive tank setup and often prefer to be alone. But just because they work well for a newbie doesn't mean you can dive in without any research. We're here with what you need to know about betta fish care and fish tanks for bettas. Here are the do's and don'ts for bettas.

What do I need to know about taking care of my betta fish?
Do research fish breeders
It all starts with the betta egg, and even the mom and dad. Just like with a puppy, you want to ensure your fishy has had a good life from hatching. There are tons of ethical breeders out there, but you can find some shady ones, too. In general, you want to avoid stores that have them crammed into tiny containers and cycled in and out every day. Do your research about local pet fish stores in your area or check out some of the more reputable ones online.

Read more
Can snakes swim? Here’s what you need to know about how these legless creatures move through water
Yes, all snakes can swim — here's how they do it
Water snake swimming through seaweed

Love snakes or hate them, they're fascinating creatures. Unlike other reptiles, snakes don't have arms or legs. Yet, even without appendages, these slitherers can move across many different types of terrain, often very quickly. They can make their way up mountainsides and climb to the tops of trees. Some even leap and glide from branch to branch!

But have you ever wondered, "Can snakes swim?" -- and which snakes can swim? Well, the answer, interestingly, is all of them.

Read more