How to Adjust the pH in Your Aquarium

The ideal pH level for planted aquariums is anywhere between 6 - 8.5

What are the effects of pH in the aquarium?

High Alkaline

pH changes in the aquarium, even if small, can have serious health effects on your fish. High alkaline, aka basic water, can affect your fishes’ gills. If your fish dart back and forth, check your pH, as this is a common symptom of high alkaline and may result in fish death.

High Acid

An acidic aquarium can result in the production of excess mucous by your fish. This is due to an increase of toxic elements promoted by acidic aquarium water. Other observable symptom include fish gasping, hyperplasia (thickening of skin and gills), and eye damage. As with high alkaline, fish death can occur.

How do I adjust the pH in my Aquarium?

How to increase the pH in the aquarium

A common method of raising the aquarium’s pH is by adding baking soda. 1 teaspoon of baking soda per 5 gallons is generally considered a safe amount for small incremental increases.

It’s best to remove the fish from the tank prior to raising the pH. Then simply dissolve the required amount of baking soda in some conditioned water and add it to the aquarium. Once the pH is at the desired level you can re-introduce the fish just like you would when you first brought them home from the store.

You should never make sudden and large pH changes, as this will have a severe effect on your fish. Start with 1 teaspoon per 5 gallons of water and slowly raise the pH incrementally. This will allow your fish to acclimate to the new tank conditions.

• add crushed coral 

• add dolomite chippings  

How to lower pH

Using peat moss is a common way to lower the aquarium’s pH. Simply put the peat moss into a mesh bag and add it to the filter. Peat moss will gradually lower the pH. With peat moss, it is likely however that your water will temporarily discolor. It should clear up over time and you can also use activated carbon to help it along.

Other methods of lowering the pH include:

  • Decrease aeration of the aquarium
  • Driftwood will soften the water and lower the pH
  • Increase CO2 levels (planted aquariums)
  • Adding RO water

What influences the pH in the aquarium?

  • The pH level can be different before and after water changes, especially if the pH of the aquarium water and the aquarium itself vary
  • Decreased aeration will lower the pH
  • driftwood will soften the water and therefore lower the pH
  • adding CO2 will lower the pH
  • high nitrates can cause the pH to drop
  • pollutants and waste in the water will lower the pH
  • crushed coral (substrate or ornaments) will increase the pH
  • hard water will cause higher pH levels
  • using a water purifier can lower pH levels (good with hard water)
  • soft water is generally low in pH
  • RO water has a pH of 6 or lower 
  • overstocked aquariums can be low in pH

Stability is the main factor, keep in mind that fish can adapt to a pH that is slightly off their preferred preference, it is the fluctuations that causes stress and fatalities.

The pH will vary during the day, it should always be tested in the morning or evening. Always ensure that the test kit has not expired.  

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Lisa Steiner

I have a 300 lt tropical tank full of fish and my ph has dropped causing the death of 3 fish in a week, what is the best way to naturally raise the ph without harming my fish.


You can use baking soda or crushed coral. Baking soda is at 1 teaspoon for every 5 Gallons (~20 Ltr) On crushed coral, place one cup in a mesh bag so you can add or remove as needed to achieve and maintain the desired pH. Once you have to correct amount you can release the coral onto the substrate.

Lisa Steiner

How is the best way to add it as can not remove the fish. Sadly just lost another one :'(

Dimitri Snowfox

Ok so i have a 55 gal tank that im planning on making into a plated cichlid tank. Currently there is crush argonite/oolite for the subrate i plan on using dirt and and peat moss as well. Is there any specific dirt that will help bring the pf down? Currently its at 8.6 but i would rather have it at 7.6-8.0 because of doing planted.


Aragonite is a crystal form of calcium carbonate and will keep your pH at higher levels. There are many varieties of plant substrates, but none will have big effects on pH, Peat moss nevertheless will lower the pH but might be hard to use as substrate.


I have a 40 gallon tank set up for for Discus fish. I have a handful of plants, although they are fairly new to the tank. My PH appears to be in the 7.6 – 8.0 range. Any suggestions on how to safely lower it? Also, I see that RO water is good. Is distilled water the same as RO?

If the aquarium setup is fairly new, wait until the cycle is completed to see where the pH will end up. If the cycle is complete, check on CO2 levels using this link
If there are elevated CO2 levels, try to air out the aquarium. Increase airflow do diffuse the CO2
After these steps, you can lower the pH by using purified water RO or Distilled, there is no real big difference besides the way the water is processed.

John hunter

I am new to the tank world but i just tested my water and i have extremely low ph and high alkaline what shold i do please help oh ya this is a cold water tank around 64 to 60 i use no heater and my room is fairly kept cool THANK U ALL AND PLEASE


It depends on what you consider low pH and high alkalinity. Some reasons why this could be is the use of buffers, in this case discontinue using buffers (pH up). The most likely issue is high levels of CO2. You can air out CO2 by heavily aerating the aquarium. You can also add some Kalkwasser which will break down the CO2 and raise the pH.

Rajan Thakur

I have 90 gallon african cihlid tank with aquarium sand and 15kgs of limestones for ph buffer but my water ph not gose above 7.9 ph
Any suggestions to raise ph upto 8.2 to 8.4


The critical point is the stability of the pH. Cichlids from Lake Tanganyika prefer a pH between 7.6 – 8.6 and the Lake Malawi cichlids between 7.2 – 8.0
In either case, your pH is where is should be, no need to mess with it.


I have a 55 gallon tank in which I had city water for my African cichlid & peacock cichlid tank and then out of nowhere they died. A bacteria formed and only 1 fish survived out of 20 and now I’m having problems getting well water to be stable to maintain the aquarium. My water is acidic in PH and very soft. The nitrate is at a .5 when it was 0 and I just had to restart the tank again. I put 2 peacock cichlid with the jewel cichlid and the peacocks both died but the jewel cichlid remains… Read more »


The pH can be raised by baking soda, crushed seashells, crushed corals, or aragonite. You can also add buffers by using Kalkwasser (lime water) which is calcium hydroxide that comes with a pH of 12

Jay M

I just set up my 55 gal planted tank and am running CO2 at 1-2 bubbles/second. The pH is down near 6. Is adding baking soda the best way to raise it?

CO2 lowers the pH, so make sure of the CO2 level. It might be too high, or sufficient with a lower injection rate. This could bring your pH back up. What you need to know is your pH and kH values, then head over to and check the table for the CO2 concentration.

Baking soda is one method, the fastest for sure. Slower but longer lasting are aragonite or crushed corals/ sea shells.


CO2 lowers the pH and is likely the cause of the drop. Make sure to check on kH as this will determine the stability of the pH

Peter m

Wow nice commets, now i know who to ask when i have a problem


Hey my PH levels in my tank have been at a steady 7 For weeks throughout the cycle…’s not all finished with the cycle but it has dropped to 6.5 and I’m worried it will drop further. I have plants and two pieces of driftwood in a 146L tank. I put CO2 in about a day ago so is that the cause? Or two much driftwood. I also have 30 fish in my tank all are small like mollies, zebra danios, tetras gubbies and two medium fish such as a pleco and a upside-down cat fish


CO2 lowers the pH and is likely the cause of the drop. Make sure to check on kH as this will determine the stability of the pH

Alfred Bon

I have saltwater tank has a reading of 0.20 ammonia, 0 nitrites, 0 nitrates and my ph level is low is there any chance to increase it i’ve added crushed coral a bit but not have been try the baking soda on it.. is my reading is safe although i’ve started it as it is and my fish are doing well. Thank you


You have to check your alkalinity levels. If the alkalinity is good, it could be a temporary shift. Marine salt mixes should provide sufficient buffering, make sure salinity is correct. The ammonia reading? Has the tank just been set up? If so, give it some time for the water to find its balance. Once complete, you can make adjustments if needed. CO2 could be another factor, try to air out the water before adding it to the aquarium.

My alkalinity is nearly 0 and my ph is 6.6 my water hardness is 300 and I’m having trouble raising ph levels to a Good 7.8 for my freshwater chiclids what do I do?


Alkalinity determines your pH. In order to increase pH the alkalinity needs to be raised as well. This can be done by adding crushed corals (1/2 tsp per 10 Gallons, or baking soda (1/2 tsp per 25 Gallons). Repeat after a few says until the kH reaches about 5 or the pH reaches closer to where you want it to be.

Erin Bee

I have a snail only tank. I added a “wondershell” to the tank (measured appropriately) and after testing the water notice the pH dropped from 7 to 6! The GH IS 180 and the KH is 0!
Upon researching I found that the wonder shell adds minerals to the water and can show false readings.
I am concerned bc one of my snails shells seems to be thinning, and nitrate levels are currently 80!
Should I try to lower nitrates or raise pH?
Help 😢


The issue is the carbonate hardness (kH)
You need to increase the kH to maintain the pH. You can use baking soda 1/2 tsp per 25 Gallons increases the kH by approx 1 (varies) or add crushed corals which is longer lasting. The level in kH you want is around 5 but it depends on your overall setup and requirements.

Erin Bee

Thank you. Since I only have a 7 gallon tank I don’t think I’d accurately be able to dose the baking soda. Is crushed coral sold in pet stores? What would be the appropriate dosing? Do you know if the wondershell screwed up the water? or is it a separate issue? The Apple snails need calcium for their shells which is why the wondershell was suggested to me initially. All other snails I’m the tank look healthy. They even reproduced! Just the one block mystery has a thinning/cracked looking shelf near the opening. Thanks again for helping. The rest of… Read more »


Sorry about all of the typos. Thanks again for responding


Two tsp of crushed corals will be a good start, and yes it is available at pet stores. The kH is what buffers the pH the higher the kH the more stability in pH. It will take a few days for you to see an increase in kH and a rise in pH, but this is a good thing.

Samantha Hughes

Hi my KH is 3°d, should be 6-10°d and my PH was 7,2 but now 8 after adding PH up. I added this as the hardness was in the danger zone according to bottle. How can i balance these levels? All other results are normal


To ensure more stability you can use crushed coral or aragonite. A little goes far, 2 tsp for each 10 Gallons. Simply place it in a mesh bag, if the results are satisfying, you can release the content onto the substrate, or keep it in the filter, whatever works best for you.

travis Nix

Saltwater aquarium
pH is at 8.4 and will raise up to 8.6-8.65
I know mixed reef is good at 8.5 as a high but I can’t seem to drop it down far enough to keep it in likable parameters.. I tend not to chase it however based off my seneye I do monitor it.. ( I use test kits as well) .. I do dose calcium and mag to help balance the alk.


This is best not to mess with. 8.6 is close enough to not worry. Fluctuations are what you need to avoid.


My ph level is so high it killed my Pleco and most my fish I only have two platys left I have used ph down and it has done nothing my water is clear there is no food waste in it when I clean it I’m stumbled as I don’t know what to do I have a 68 litre tank it’s got to the point the foam pads in the top of the tank have been deteoriating lately too please help


Carbonate Hardness (kH) measures the buffering capacity and indicates how stable the pH will be. The higher the kH the more stable the pH. If your pH is persistent high despite adding pH down, you kH is likely very high. Reverse osmosis (RO) water has no hardness and can be used to lower the kH.

Nancy K O'Leary

The pH test color chart scale that came with my pH test kit had a number scale of 7.6 to 6.0 in 0.2 increments. My aquarium water was tested at 7.6 or higher according to the color chart. I added two applications of pH down (a 9.6% sulfuric acid solution) per day for two weeks which did NOT change the pH of the water but eventually all of the fish died. So why didn’t the pH change and why did the fish die?


Carbonate Hardness (kH) measures the buffering capacity and indicates how stable the pH will be. The higher the kH the more stable the pH. If your pH is persistent high despite adding pH down, you kH is likely very high. Reverse osmosis (RO) water has no hardness and can be used to lower the kH.

Joanne Murdock

I don’t know if I’m doing it right. The pH for my tropical aquarium is 6 or lower. Acidic. Its destroyed my plants.. Do I use pH up or pH down to get it to 7?

pH Up raises the aquarium’s pH, pH Down lowers it.


Ph up. Just about half teaspoon in 100 litres of water will change it slowly. Check it every three to four days

Mel w.

The article is mistaken. Increasing aeration usually raises ph, not lowers it; the reason is because increasing aeration helps raise the oxygen level in the water.
Carbon dioxide lowers ph, oxygen raises it.


It says “Decreased aeration will lower the pH” not increased.


Read carefully please.

Sherry Yurchisin

Is there a fairly quick way to lower the acidity of a freshwater tank? I need to move some fish from a tank with high nitrites before they die and the only tank that could work has off the charts acidity. I’m at a loss as I’m new at all of this.


Lets assume your aquarium is cycling, or adjusting due to new fish or other circumstances? Add a pinch of salt to ease the nitrite poisoning. Watch the fish closely and perform a water change 10-20% per week. Keep in mind that the aquarium you place the fish in will also start cycling with ammonia/ nitrites being involved as well. Any pH level below 7.0 is considered acidic, not sure why you would want to lower the pH. Lets assume you have low levels (acidic) in the aquarium and need to move more towards the neutral area? Use baking soda. One… Read more »

Pamela A McCue

He said lower the acidity, not lower the PH. I gather he meant decrease the acidity; raise the PH.

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