Maintaining your fish tank is a lot more than simply keeping the water clean. You need to know about the chemical composition of the water and how this affects the health of your fish. In particular, you should understand what the pH level of the water means and what you can do to change it. Once you know what causes high pH in aquarium water you are in a position to do something about it.
So, if you are wondering what causes high pH in a fish tank all you have to do is read on. We have researched all the complicated chemistry and read the expert opinion so that we could condense it into this easy-to-understand guide.
A Quick Guide to Aquarium pH Level Science
When you see the pH of a substance referred to it is describing how acidic or basic (alkaline) a substance is. The pH scale ranges from 0 to 14 units. pH levels of less than 7 are acid and those above 7 are a base. A pH of exactly 7 is called neutral
It is actually a measure of the free hydrogen ions in the water – if there are more hydrogen ions it is acidic. The aquarium’s pH indicates what chemicals are present in the water. Most fish need a specific pH in an aquarium to stay healthy.
What is the Correct pH Level for Fish Tank?
Unfortunately, there is no single correct aquarium pH level as it depends on the fish species that are living there. This is why you have to be careful about what fish you keep together in the same tank. In nature, fish would live in ponds, lakes, rivers and the sea and all of these bodies of water have a different pH. The biological processes of each species are adapted to suit the environment where they live so you must replicate that in the aquarium water to keep your fish healthy.
In general, saltwater fish like alkaline water with a higher pH of 8 or above. Freshwater fish from rivers and lakes however need freshwater tanks with a pH of between 5.5 and 7.5. As an example, the popular Neon tetra fish need pH levels of between 5.8 and 6.2. Goldfish need a pH of 7.5 to thrive.
Is Fish Tank pH Level Important?
Yes, it is very important! Changes to the pH of your aquarium water can cause significant health problems and even death as fish’s bodies have evolved to survive within a narrow pH range. Sudden changes can be especially hard for fish to cope with. For example, a sudden rise in pH will increase the toxicity of ammonia.
Here are some occasions when your fish are particularly vulnerable
- When you have young fish
- When you have sick fish
- When setting up a new aquarium – find out the pH of your tap water or other water sources
- When adding new fish to your aquarium – Neon Tetras are very sensitive to sudden changes in pH when they are moved from one tank to another
- When planning to breed – many fish will only breed at a particular pH
- When introducing a species that is particularly vulnerable to pH changes e.g. the Discus and some other cichlids
It is very important that you check the pH regularly in your aquarium.
When to Check the pH of Your Aquarium
The next question is when should you check the ph of your fish tank?
Ideally, the pH in an aquarium should be tested every fortnight but you may get away with it every month. This will allow you to notice trends in the aquarium water pH before they start to cause any problems. It is helpful to keep a record of every reading and the date that it was taken. This needs to be done for all of your fish tanks if you have more than one. A top tip is to do the testing at the same time every day. Results can be different in the morning and evening so you can only compare them over time if you test at the same time of day on every occasion. Most experts agree that the afternoon is best.
There are other exceptional occasions that should prompt you to test in addition to your fortnightly routine. If one or more of your fish is sick or dies you should always test the tank water and the same applies if you have added medication. Test the pH inside the tank before, during, and after the treatment and take appropriate action if it is not suitable.
It’s also a good idea to check the pH level of the aquarium water before you buy any new fish. Find out the pH of the water at the local pet store where you are purchasing your fish and make sure that your own aquarium water does not vary from this by more than 0.2 units.
How to Check Aquarium pH Level
The simplest way to check the pH level of your fish tank is to buy a home testing kit. It will come with full instructions. All you have to do is add some of your aquarium water to the test tube and add a drop of the special testing solution.
The water’s pH will be indicated by the color of the water and you can compare this to a chart that is also provided. Other people prefer to use pH litmus strips which are a special type of paper that turns a certain color when exposed to water with different pH ranges.
A pH that is too high is always more dangerous for fish than a pH that is too low.
What Happens if the pH is too High?
As well as detecting a high pH using the above test, there may be other signs of high alkalinity (base) in the aquarium. The first telltale sign is a sudden and rapid growth of green algae which is noticeable on the walls and objects inside the tank. Rapid algae growth makes the water toxic. Often, the aquarium fish start to behave in an unusual way with chaotic swimming and the production of excessive amounts of poop.
Once your fish begin to appear sick and diseased, it can be a sign that the high pH is significant. High pH levels prevent a fish’s gills from being able to work properly. Gills are like lungs in other animals and fish need them to get oxygen into their body. If fish do not get enough oxygen, they die.
Also, water with a high pH damages the mucus membranes that form a protective layer around the fish’s body. You may notice growths on the tails or fins as pathogens are able to multiply.
Ammonia toxicity is a major concern especially when the pH of the water is higher than that of fish blood. This generally happens above a pH of 9.
Causes of a High pH Level in an Aquarium
So, what causes pH to rise in aquariums in the first place? There are a number of potential reasons.
Substrate, Stones, and Decorations
Some types of substrate and stones and even decorations can raise pH levels. Objects that are calcium-rich (such as limestone) can be problematic because calcium will dissolve into the water increasing the pH.
A lack of carbon dioxide can cause the pH in an aquarium to increase. If you are over aerating the tank, too much carbon dioxide may have been removed which raises the pH. More carbon dioxide in the water will lower it again because CO2 combines with water to form carbonic acid and a lower pH.
Plants in Fish Tanks
Take care with the type of plant species that you add to the aquarium. Aquarium plants can cause a high pH level if they are too dense and you also have to remove dead plants regularly. Plants can trap carbon dioxide and nitrates which causes the carbon dioxide levels and nitrate levels to fall which raises pH levels.
Do you add tap water to your aquarium? This could be causing the problem because tap water often contains alkaline chemical substances and metals which can raise the pH in an aquarium. It is not good practice to add untreated tap water to a fish tank. However, you should also not add untreated water from boreholes or streams or even rainwater because all of these do not have a neutral pH and will therefore affect the pH levels in the tank.
Have you checked if your filters are working correctly? An inadequate filtration system will mean that leftover food accumulates in the tank. These old fish food particles decompose and raise the pH levels. Check that your filter is working correctly and does not need cleaning.
Perhaps you have tried adding baking soda to increase the pH levels but this has resulted in an overly alkaline water? Baking soda should be dissolved in water first and added very carefully and regularly so that your fish can adapt.
If you have algae growing on surfaces within the tank, it can have a big effect on pH levels. When in the light, algae photosynthesize which produces a lot of oxygen but uses up the CO2 which, in turn, causes a high pH.
How Can you Lower pH Levels in Your Aquarium?
Once you know that your pH levels are too high, you need to take steps to reduce them to safe levels. Here are the most effective methods that the experts recommend:
Add Peat Moss
You can tackle a high pH by placing peat moss in your aquarium. Peat moss is a natural substance that is slightly acidic and therefore reduces the pH level. The only issue with using peat moss is that it can make the water look a bit yellow. You can place peat moss inside the filter or in your substrate or inside a filter bag to stop it from floating.
Only use peat moss from a pet store that is produced for aquarium use and is 100% natural. Soak it in clean water for four days before placing it in your aquarium. Start off with a small amount as sudden and large changes in pH levels are not good for aquatic pets.
Add Other Natural Stuff
Driftwood looks fantastic in a fish tank as well as reducing the pH level. You could try adding one or two pieces but it must be completely natural and must not contain any dyes or resins. There are many different types including cholla wood and tree root. It also has to be prepared correctly before you put it in by removing debris, washing, sterilizing, and curing. Alternatively, you could purchase ready-prepared driftwood from a pet store.
Add Almond Leaves
Natural almond leaves are great at reducing an aquarium’s pH and also look great. In addition, their anti-inflammatory and anti-bacterial properties produce a healthy aquarium environment by preventing lots of diseases. They also provide a space for fish to hide away when they want to. You can get them from many pet stores.
Reverse Osmosis Filter
A reverse osmosis water filter (RO water filter) is one of the most effective ways of reducing pH levels in a sustainable way. However, it is also one of the most expensive methods. It will carefully filter the water and reduce contaminants – the filtered water is pH neutral. You may have to replace filters from time to time.
A dirty tank will often have high pH levels so make sure that you clean it regularly. Make sure it is free from waste and change your filter often.
Finally, try to avoid adjusting the pH levels in your tank with chemicals. They cause rapid changes in pH which are not good for the fish and are not sustainable. Wherever possible, natural methods are preferable.