How to Lower Alkalinity in Fish Tank Effectively?

how to lower alkalinity in fish tank

Just as general hardness, alkalinity (or carbonate hardness, a.k.a. KH level) also relates to mineral ions inside your tank water. Once it becomes higher, it’s time to know how to lower alkalinity in fish tank without harming your pet fish.

This action is vital as high alkalinity leads to breathing difficulties in fish from the toxic ammonia compounds. Furthermore, the fluctuation in water conditions can also cause serious stress and even death.

Fret not, I will show you what causes your issues (such as decorating plants or rocks) and the best ways to treat high alkalinity in fish tank in this article. Scroll down now!

Ways to Lower Alkalinity in Fish Tank

#1 Change/Dilute Your Tank Water


Fish create a large amount of waste, and when the waste decomposes, it will inevitably affect the water quality and raise the alkalinity. Therefore, doing minor water changes each week to lower alkalinity and pH is a way to go.

  1. Replace 10 to 15% of your tank water with distilled water, rainwater, or reverse osmosis water (RO water) with lower alkalinity. Stick to the same water-changing ratio each time to avoid putting more pressure on your fish’s health.
  2. Vacuum the gravel/substrate every time you do the water change helps you to keep your tank water soft longer.
  3. Check the alkalinity level afterward to see if it’s within acceptable range. If not, consult the methods below.

#2 Use White Vinegar or Lemon Juicelower-alkalinity-in-freshwater-fish-tank

Since alkalinity represents the alkali characteristics of the water, you can fix alkalinity in a fish tank by adding additional acidic liquids (like vinegar and lemon juice). However, the result of this method is only temporary, so you should look for other suggestions in the long run.

What to prepare:

  • pH level test kit
  • White vinegar (or lemon juice)

Detailed ways:

  1. Remove any living creatures out of your fish tank. Place the fish in a clean container with water from their tank.
  2. Add white vinegar (or lemon juice) into the tank bit by bit.
  3. Constantly test the pH and alkalinity levels to detect the changes.

#3 Plant More!

Aquatic plants consume carbon dioxide and release oxygen into the water; which is how this method assists you to reduce alkalinity in aquarium. Other types of plants (such as Egeria) lower alkalinity in aquarium by absorbing the mineral ions, like calcium or else.

In either case, it’s best you refer to the aquarium plant suggestions at the pet store to see which one is suitable for the fish and your specific tank setup.

Remember to remove dead plants from the tank as the ammonia emitted might drop the pH levels and impair the health of your pets.

#4 Use Peat Moss or Natural DriftWood


Peat moss and driftwood can help you adjust your tank’s alkalinity naturally without harming your pets. Therefore, this method is most suitable whenever your freshwater aquarium alkalinity too high.

However, the driftwood you use must be natural because treated ones can contain some chemical harmful for your fish. For peat moss, ones that are 6 months old are preferable as it’s less likely to increase the pH level compared to the “younger” variants.

What to prepare:

  • A mesh bag (if you use peat moss)
  • 6 months old peat moss (or a piece of natural driftwood)

Detailed steps:

  1. Put the peat moss into the prepared mesh bag (skip this if you use driftwood instead).
  2. Submerge the whole thing into tank water and wait for the magic to happen.
  3. If possible, plant aquatic plants onto the driftwood and double the positive effect.

#5 Employ A Reverse Osmosis (RO) Filtration System


You will never regret investing in a reverse osmosis filter because it will not only help you to lower alkalinity in freshwater fish tank but also in saltwater ones.

Basically, the machine filters out any excess contaminants, minerals, or metals, meaning it can stabilize the tank water’s quality more effectively. Moreover, you can adjust the machine’s settings to meet the requirements of your pets.

All in all, the next thing to do is to consider and purchase one for your fish tank.

Alternatively, you may also use a chemical filter instead of a RO filtering system to remove excess mineral ions. However, some varieties may be dangerous to your fish, so use caution when selecting a product for your tank.

What is Alkalinity and Its Effects?


Basically, alkalinity is a vital index representing the bicarbonate concentrations within your tank water (or any other kind of water).

Alkalinity strongly relates to the water’s pH level, so its fluctuations also directly affect your aquatic pets’ lives. Depending on the situation, it may be only your fish’s looks that are damaged (ragged tails/fins). In the worst-case scenario, however, if you fail to reduce alkalinity in the fish tank, your beloved pets might die.

Why is the Alkalinity High in the Aquarium?

There are multiple reasons why the alkalinity is getting higher in your fish tank and here are some possible answers for you:

  1. Using aquatic plants that trapped carbon dioxide (which might create slime/algae on rocks or glass and unexpectedly raise the pH level up).
  2. Aerating your tank with the wrong kind of air stones (leading to carbon dioxide leaking and raising the pH level).
  3. Using unconditioned tap water that has excessive minerals.
  4. Using too many calcium-rich stones/rocks as decorations.

As a devoted fish keeper, you should monitor the alkalinity as frequently as possible to avoid any sudden drop or growth and come up with a prompt solution.

Helpful Tips/FAQs

What are ways to test alkalinity in fish tank?

I strongly advise you to use an electronic pH meter, a digital pH pen, or an aquarium pH test kit. It’s because the alkalinity level has a reciprocal influence on fish tank water’s pH level (helping to stabilize the tank’s pH and so on), so you can monitor the alkalinity changes by testing the other one.

Among the suggested products, the aquarium pH test kit is the most affordable and comes in a variety of types for use in saltwater aquarium (or freshwater ones).

Otherwise, you can also employ pH test paper or hydrion pH paper; but these tools provide less accurate results.

What should the alkalinity be in an aquarium?

It should be around 70-140 ppm or 4-8 dKH.

In case you use the pH level kit to monitor the alkalinity, it depends on your pet’s types. The range of 8.0-8.1 is good for saltwater species and 5.5 – 7.5 is the ideal point for freshwater fish. For example, the recommended alkalinity level in betta tank is 6.8-7.5.

However, some freshwater creatures, such as cichlids or loaches, can tolerate when the alkalinity level reaches up to 7.8.

Will high alkalinity kill fish?

Obviously yes. Not only leading to fish death, but the high alkalinity can also make your pet fish become more susceptible to diseases, vulnerable to infections, or get more aggressive.

How to deal with low alkalinity in fish tank?

Here are some recommendations once your tank water has lower alkalinity than usual:

  1. Fix it with baking soda: Remember to use only 1 teaspoon of baking soda (dissolved with water beforehand) for every 10 gallons of tank water.
  2. Use crushed seashells/coral: Beginning with only 2 pounds of crushed seashells/coral per 10 gallons of tank water is the best and notice to check the pH level later on.
  3. Change the tank water: To avoid water shock reactions in your fish, refresh no more than 20% of the tank water each time.


I’m hoping that the subject of “how to lower alkalinity in fish tank” is no longer one of your concerns as I’ve shown you several solutions to the problem. Feel free to give me feedback if you still have any other questions about it.

Otherwise, in case you have other helpful tips, don’t hesitate and share them with us in the comment section. Your constructive comments will become my motivation in future work. Thanks a lot in advance!