A lot of fish will only thrive if an aquarium’s water is just right. This can sometimes mean adjusting the water’s pH level if necessary. While this can be achieved with store-bought chemicals, there are natural ways to raise and lower pH levels in your aquarium that are more gentle on your fish.
The “pH” level of your aquarium is a measure of the hydrogen ion activity in the water. Not exactly the same as measuring concentration, the pH level is, instead, a measure of activity, with the “pH” representing the “Power of Hydrogen.”
It is measured from 0-14 with numbers up to 7 representing alkaline solutions and above as acidic, with 7 itself being neutral.
- 0-6 Alkaline
- 7 Neutral
- 8-14 Acidic
If the hydrogen ion activity in your fish tank is too high or too low, the health of your aquarium’s fish, invertebrates, and plants. Store-bought fish may already be acclimated to the pH level of tap water.
However, if the fish, plants, or other life were bought from a different area, collected in the wild, or you’ve recently moved home, the tap water is likely to be of a different pH level than what they’re used to. These sudden changes in pH level can be damaging to your aquarium bio-system.
Over time, the pH level of aquariums tends to move lower down the scale, too, towards alkaline. This is due to the build-up of organic waste matter and the depletion of mineral buffers in the water. Mineral buffers help water resist pH level changes but diminish over time.
There is no correct pH level for a fish tank. The correct pH level is one that is suitable for your fish, plants, and invertebrates.
That said, most aquariums feature fish and plantlife and each prefers a variety of different water conditions, including pH levels. This usually means finding a suitable compromise on a pH level.
- Freshwater fish: 5.5 – 7.5 pH
- Saltwater fish: 7.5 – 8.0+ pH
You should always research if any of your tropical fish species have any special requirements. Most fish can acclimatize well to small differences, however, but irreconcilable pH preferences can occur.
Before adjusting the pH level of your aquarium, you’ll want to know what you’re dealing with.
You should check the pH of your water using a pH testing tool. These come in various forms with the most common now being:
- pH pocket pen: reusable electronic measuring device.
- pH paper: cheap but less accurate and based on color judgment.
- Wide range pH testing kit: ideal if you aren’t sure of your tap water’s natural pH level.
- Freshwater pH test kit: more accurately measures lower pH levels
- Saltwater pH test kit: more accurately measures higher pH levels
Dissolved oxygen naturally raises the pH level of water, without the need for chemicals, by lowering the amount of carbon dioxide present.
This is because high concentrations of carbon dioxide allow carbonic acid to form which, in fact, can lower the pH level of your water. Increased oxygen levels can prevent this.
Oxygenating your water is easy, simply raise your filter slightly above the water level to introduce some oxygen into the pumping process. While there are dedicated filter pumps that can do this, only very large aquariums would require such a solution.
One of the biggest culprits in lowering pH levels is driftwood. A lot of aquarium owners introduce driftwood to their tanks and find their water moves quickly towards the lower end of the pH scale.
This is because of tannins and tannic acid released by driftwood and bogwood. These cause water to become more alkaline fairly rapidly.
If you’re trying to prevent your tank pH level from going any lower, you will want to first boil your driftwood before introducing it. This process should be repeated regularly as the decay of the wood will cause further tannic acid to form.
Changing water regularly is part of your aquarium maintenance but can also help prevent drops in pH levels. As the water in a tank naturally moves towards alkalinity over time, removing and replacing water is one way to maintain a pH level.
This is because it removes the pollutants and decaying organic matter that decrease hydrogen ion activity.
Simply remove 15-20% of the tank’s water every 2 weeks and replace it with pre-treated water. While you may be tempted to replace more water at once, this can induce shock in fish and even result in their death.
For pH levels that are really low, you can help bring them back up by using a few pH raising materials in your substrate. These include:
- Crushed coral
- Cichlid shells
These can be crushed to a suitable coarseness and added to your existing substrate. Over time, these can help keep pH levels topped up in areas with more alkaline water.
While bad news for those looking to raise the pH levels of their tank, the tannins and tannic acid given off by driftwood and bogwood are great for creating a more alkaline aquarium.
The tannins released into the water bind with minerals such as calcium and magnesium and prevent them from upsetting the pH level of your tank.
Aquarium safe types of driftwood include:
- Sumatran (mangrove roots)
As well as driftwood, certain kinds of leaves can be used to lower your aquarium’s pH level. These leaves absorb ammonia, and nitrates, kill bacteria and tend to have lower tannin levels than driftwood.
- Almond leaves
- Oak leaves
- Cappata leaves
Simply add these leaves to a dedicated pot or shred them and mix them with the substrate. These will give your water a lower reading within a week.
Peat moss releases a lot of tannins and lowers the pH level of water considerably, fast. You’ll want to introduce it slowly, therefore, and measure your levels as you go keeping an eye on the color of your water which may become more yellow.
While this discoloration is generally fine for the fish and plant life, some owners dislike the change, and using peat moss in collaboration with other methods may be beneficial.
Peat moss works fast so check pH levels every few hours after introducing 1-2 tablespoons.
Being a bio-system with mineral buffers diminishing and organic, decaying matter accumulating, a healthy aquarium will naturally move towards the lower end of the pH scale over time.
For this reason, if you’ve only just added water to your tank and your fish and plant life seem generally okay, it could be worth simply waiting a little while for the tank’s pH level to lower itself.
Fish especially are hardy and can acclimatize to water quickly. Hastily adjusting the pH level of water can often be worse than simply leaving it be.
Finally, whether you’re trying to raise or lower the pH level of your aquarium, you can always adjust your water source. While your tap water may be unsuitable for your fish, a friend or family member’s might be just the right pH level for your tank life. Filling a few containers up with their tap water might well be the easiest solution should this be a readily available water source to you.