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.

Clear cloudy aquarium water, remove nitrates and simplify aquarium maintenance

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.

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:

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

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
  • Increased 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
  • overstocked aquariums can be low in pH

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30 thoughts on “How to adjust the pH in your aquarium

  1. Danielle says:

    Hi i have cycled my tank and had the water tested it is ready however my ph is high despite using treatment in the water. We used love fish tap safe. The ph is still reading 8. Is there anything else i can add to lower the ph before i add guppys. Thank you

    • Thilo
      Thilo says:

      Do keep in mind that the pH fluctuates slightly throughout the day. Also if you had it tested, the time from when you remove the water sample, to the time when the water is tested, pH can change. Testing pH should be done on a regular basis, so it is a good investment to have a pH test kit on hand. With that you can also test the water you are using for water changes to determine if the pH is high from the water source, or if the cause of the higher pH is within the aquarium.

      Changing the pH value can cause instability and cause more issues. A pH of 8.0 is not really that bad for guppies and even with the pH being slightly out of the comfort zone, it should not be a problem.

  2. Helen says:

    I’ve recently added baking soda to my 50 gal tank to increase the pH. I used half the recommended 1tsp per 5 gal amount and found my pH to increase from 6.2 to 7.2! I had to quickly add drops to my tank to lower the ph as this increase is huge. If you are trying to increase the pH I suggest you add 1 tsp per 25 gal not one per 5 gal as this steep of an increase may shock the fish.

  3. Heng says:

    yesterday i have bought the RO filter set(brand :micron 50gpd) the water goes through the filter but im not satisfied with the high PH but the TDS result is very good we can get 3 PPM but the PH is 9.0 What is the reason for this is it my filter or because of other reasons? our house tap water does not go through filters the result is 120 PPM,PH is 7.0

    • Thilo
      Thilo says:

      If you have an alkaline water filter included in your set, it will increase your pH. Please check with the manufacturer for details.

  4. Angela says:

    One of our fish died and after testing the water realised the ph level was around 12 plus the pump wasn’t working. Changed the water, and retested it after adding water conditioner and instead of lowering it, it’s around 14 now. New pump is on the way. What would you recommend? I thought I was helping but seem to have made it worse.

    • Thilo
      Thilo says:

      The pump is definitely a vital part and might just solve, or at least contribute, to correct the cause that killed the fish.

      I have doubt about your pH readings. A pH of 12 is that of bleach and there is literally no natural way for the pH to reach levels of 12 or even 14.
      Your test kit might be expired or the chemicals have been compromised and provide false readings. I strongly recommend to purchase a new pH test to see where the actual values are.

  5. Ano says:

    Mine was because of aeration. Whenever I try to turn on my bubbles maker, the following day my fishes looks stressed and ph drops.

  6. DIANA L BROCK says:

    I can’t keep my ph levels lower than 6.8 so I used baking soda, 3 teaspoon for 20 gal tank. It shot up my ph to 7.6 and possibly higher. Went to feed them only find 2 guppy dead. I exchange 2 gal of dechlorinated water. It didn’t change not a bit. Now I’m going to change 4 gal of treated water cause I don’t know what else to do.

    • Thilo
      Thilo says:

      It is not the level of the pH that caused issues it is the rapid change. If you attempt to lower the pH, please take your time. You can use distilled, or R/O water one gallon at a time to achieve that.

      6.8 is actually an acceptable level for guppies. Check on the carbonate hardness (kH) which will indicate the stability of the pH. Your current level of 7.6 is also within acceptable parameters. I would just leave the pH alone, it will adjust itself. Again kH is the determining factor.

  7. Nicki says:

    Please do not use any baking soda!!!!!!!I’ve spoken with many fish experts and baking soda is used to euthanize fish in most pert stores. It deprives them of oxygen. IT WILL NOT FIX your Alkalinty problem.

    • Thilo
      Thilo says:

      Baking Soda is harmless and has many benefits in the aquarium. Yes, it can be used to anesthetize a fish and in consequence euthanize a fish, but so can many harmless substances. It is the quantity that makes it beneficial or detrimental.

      The dosage to anesthetize a fish varies given the species, but used at 1000 mg/ L it is a fish anesthetic but insufficient to euthanize a fish.

      In a standard 20 Gallon aquarium, you would need to use 76000 mg/L to anesthetize the fish, but only a fraction is needed to increase the pH quite effectively and without any short or long term harm. On the higher end it would be 1500 mg/L to raise the pH in a 20 Gallon aquarium.

      In conclusion: baking soda is quite safe to use.

  8. Deborah York says:

    bought algone about a month ago,have changed 25% to even 50% of my 30 gal. tanks water & have used two of the algone packs (bought 6pk box) & still my nitrates are over 40ppm, its not working…what’s goin on with my tank!

    • Thilo
      Thilo says:

      Algone does not influence the pH levels. The article above just offers solutions depending on weather you want to lower or increase your pH level.

      In reference to pH, higher nitrates are not really in direct relation. Nitrates likely indicate less than ideal water conditions probably caused by a lack of maintenance, overfeeding and or overstocking. These “symptoms” can of course in part influence the pH and vice versa.

      Large or frequent water changes should be avoided in general. Water changes can influence the pH depending on the water source, but large water changes will effect the pH regardless of the source.

      Alkalinity (buffering capacity) is what you should test for to check the stability of the pH.

  9. Lauren says:

    I have very hard tap water, and thus a very high pH. Would mixing some filtered/distilled water with my tap water at each water change be a good solution, or would peat moss be better? I’ve been keeping African cichlids so the high pH hasn’t been a problem, but I’m setting up another tank for fish that need a lower pH.

    • Thilo
      Thilo says:

      Distilled water will work so will RO water (available at pet stores) Distilled water is around or sighly lower than pH 7.0 while RO water is well below pH 7.0

    • Keith Procter says:

      Adding RO water won’t change the pH by much, if at all. Since the pH is driven by the aqueous “contaminants”, and those will still be present at about the same concentration. The contaminants in your case are likely mostly calcium and similar elements that cause the pH to be high, and the water basic. What adding RO water will do is reduce that alkalinity of the water. Alkalinity is a measure of how difficult it is to change the pH, or how stable the pH is. The higher the alkalinity the more stable the pH, which is a good thing, if the pH is what you need it to be.

      The best option is to use RO water and a pH 7.0 buffer (or slightly higher), but if you don’t have RO water available, then tap water with more buffer. The buffer is a mixture of complementary chemicals that work together to stabilize the pH.

      On the flip side, if you were looking to raise and stabilize the pH, then a marine or cichlid buffer is better than adding baking soda because it stabilizes the pH. You can use baking soda to approach the target pH, but having a buffer makes it harder for the aquarium to move away from that target.

  10. Dmitriy Yakovenko says:

    Thanks a lot for help with PH issue. I tryed many different fancy potions, lol, but can’t fix the problem. Backing soda works! Fish became a life in a couple hours. Amazing! Thanks again.

  11. EW says:

    I have Banded and Gloriosis sunfish with a PH of7.8 or possibly higher. Will natural Peatmoss bring down the PH to the 6is range–Say 6.2 tp 6.8. I’m currently using rain roof water as the liquid source.

    • Thilo @ Algone
      Thilo @ Algone says:

      Yes, peat moss will lower the pH of the water, so will R/O water (mix it with regular water to achieve the pH you desire). Please take your time in lowering the pH as it might shock the fish/ inhabitants if done to abrupt.

  12. Cecilia says:

    I have 2 goldfish in my 10 tank. Sadly, they both died, after just one month. My record was not so bad before, having had a fantail ryukin survive a full 5 years. Then I got the new goldie plus a bulging eyed black one, who had bubble eye disease –>For ryukin goldies, the PH level is supposed to be high, yes? It is now at 7.0. Supposed to be at 7.5, blue. Should I just add 1 teaspoon of baking soda, twice? Before getting new fish?

    • Thilo @ Algone
      Thilo @ Algone says:

      Baking Soda will increase the pH, but crushed corals or sea shells are more of a long term solution. Use 1/2 cup for every 20 Gallons and make adjustments from there. Corals and sea shells release calcium carbonate, which increases the pH level.

  13. Keith says:

    I have discus in my fish tank. My ph is 7.6 I tried peat moss , driftwood,I don’t want to try chemicals because I want to do everything natural.also I have plants inside my tank.

    • Scott @ Algone
      Scott @ Algone says:

      Using peat moss and/or driftwood are the most common methods of naturally reducing pH in the aquarium. If those didn’t work you can also consider using R/O water as this can help stabilize and keep pH at a constant. Carbonate hardness (KH) of the water determines how stable your pH is. Lower KH will result in lower pH. You can lower the KH with R/O or distilled water. We generally don’t recommend this unless it is absolutely necessary. Because big swings in pH are usually fatal for fish, only very small incremental changes should be attempted. If you take this route be sure to monitor the water parameters carefully, and adjust the pH very slowly over the course of days.

  14. Pingback: Relationship between pH value and CO2 in aquarium - Aquarium Talks

  15. Thilo @ Algone
    Thilo @ Algone says:

    Aeration is listed as a part of several options to lower the pH not as the exclusive solution. The pH is more complex and the solution to lower the pH needs to be applied based on the individual circumstances. Aeration itself does not have a significant impact on the pH within the aquarium.
    In your example of aerating a bucket of water, if the pH rises, it simply means that the pH is unusually low for the alkalinity level.

  16. Kc says:

    Increasing the oxygenation of water without adding co2 raises the ph of tap water, it does not lower it. When you put an airstone in a bucket & fill it with tap water with a ph of 7.8 & leave it aerating over 24hours the ph goes up not down.

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