Does Water pH Level Affect Guppy Fish?


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Guppies are a great pet for beginners and also for experienced fish keepers. I often get these questions from beginners whose guppies are dying:

Does the pH level of water affect guppies? Are they sensitive to changing pH levels? Guppy fish will die off too low or too high pH levels?

Guppies are a really hardy fish and they can accept a wide range of pH levels. However, the best is to keep them in basic water with a pH level between 7 and 8. Guppies and in general livebearers don’t like soft acidic water.

How to Measure the Water pH Level?

Measuring water pH level is not rocket science. In order to determine the pH level, you need to get a pH tester strip or a digital pH meter. I use the digital pH tester, although it is a bit more expensive than the strips. The digital tester might be a better choice for the long run because strips will expire after some time and will not show good results anymore.

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How to Lower pH Level?

If you are using tap water in your aquarium that has a pH level greater than 8, you should consider lowering it. There are few options you can do to lower the pH level of your tap water.

A good option to lower the water pH level water is to keep it for a few days in unsealed jugs or buckets. I’ve experienced that in just a few days the pH level of aerated water can drop from 8.5 pH level to 8 or lower.

If you can’t keep gallons of water around, you can use live plants in your aquarium. Guppies and fish love live plants, so use them with confidence. Plants help in stabilizing pH levels. I’ve noticed that water in aquariums with live plans has a lower pH level than in aquariums with plastic or no decoration.

You can use some chemicals to lower the pH level. Adding 2-3 drops of Seachem Prime to each gallon of water, can help in reducing pH levels. Prime is a great product that will neutralize chlorine, chloramine and other heavy metals found in your tap water.

Adding driftwood to your aquarium can also help in lowering the pH level.

Injection of CO2 for planted aquariums will also decrease the pH level on aquarium water.

RO/DI water has a pH of 6. Mixing the tap water with RO/DI water can help lower the pH level. Add RO water slowly to tap water and test mix it well. Test the pH level and adjust the temperature, before adding it to your aquarium. In order to make RO/DI water, you need to purchase a RO/DI water system.

How to Increase pH Level?

Low pH level is rarely a problem in freshwater aquariums, but it can happen. Here are some good options to raise the pH level in your aquarium:

Adding 1 tsp of baking soda to every 5 gallons can help you increase the low pH level in the aquarium water. Before dissolving the baking soda, remove the fish from the aquarium. Wait 30-60 minutes before adding the fish back to the aquarium. Measure the pH level again, before adding the fish.

The substrate can also be a huge factor that contributes in decreasing the pH level. Remove the substrate and add coral, limestone or Texas holey rock. These minerals and rocks will help increase pH levels. Remove fish when working with the substrate, because it can be very stressful for them. Measure the pH level of your aquarium once a week, and test the results.

Adding 1-2 seashells per 1 gallon can also raise pH level. Seashells contain carbonates that will slowly dissolve in the water and will help in raising pH levels. Seashells can be purchased at most pet stores or online from Amazon. Do not use seashells that are used for home decoration or are painted. These can contain chemicals that will harm or kill your guppy fish.

If you have driftwood in your aquarium, consider removing it to see if that is causing the pH level to drop. Often this can be a good solution.

Aquarium water tends to drop in pH over time. If you have live plants and you are injecting CO2, pH level will decrease at a faster rate. Doing regular water changes can help you keep pH levels at normal ranges.

Aquarium salt will also raise the pH level in your aquarium. It will also increase the salinity that some fresh water fish will not tolerate. Fortunately, guppies can accept a small level of salinity. Salt is also beneficial for treating some diseases such as ich or other bacterial infection. Add 1 tsp of aquarium salt per gallon. Do not use iodized or table salt!

What Influences the pH Level in Aquarium?

There are many things that can affect the pH level of your aquarium water. I’ve mentioned a few of the above, but will summarize them in the following list:

  • Water aeration will lower pH level
  • Drift wood will soften the water and will lower pH
  • CO2 and live plants will lower pH level
  • High nitrate levels can cause pH level drop
  • RO/DI water will lower pH level
  • Too many fish can contribute in dropping pH level
  • Aquarium salt will increase pH level
  • Crushed coral, seashells, limestone substrate will increase pH level


Whether you need to raise or lower the pH level in your guppy or any fresh water aquarium, now you know how to do it.

I relay hope that this article has helped you to adjust pH level. However, if you have any questions, please let me know in the comments below. I will try to answer you as fast as possible.

Happy fish keeping!

Updated: October 12, 2021
Questions & Answers
  1. Hi
    I’d like to know the normal water parameters of growing the guppy fries. They’ve been struggling from pinned tails once they reach to 1st month or more. pH level has always been around 8.0
    No other check-ups have been provided btw.

    P.S: the tank is decorated with live plants

    1. avatar

      Hi! The pinned tails is not due to pH level. Actually a pH level of 8 is good for guppies.
      In my opinion the pined tail in guppy fry is caused by ammonia spikes. As the fry grow, they produce more and more waste and the tank / filtration is not able to handle the raising ammonia level.
      Live plants are a great option to reduce ammonia, nitrites and nitrates. I don’t know how densely your tank is planted; probably you need to add a lot more live plants, especially fast growing plants. Guppy-grass is a really good live plant that is able to remove a lot of nutrients from the water.

    1. avatar

      You should adjust pH level slowly and try to avoid any drastic changes in the water chemistry. Guppies are hardy fish, but it is best to acclimate them slowly.

  2. Hi there GE,
    I have high ph tap water and initially didn’t know I had to adjust it. I have “pH down crystals” (1/2 teaspoon per 100L) and was changing 10% of water in a 20L tank daily and bringing the ph of the new water down to 6.8 and adding it. I did this for a week and it made next to no difference.

    I’ve now resorted to mixing a half a pinch of crystals into a small cup of water and adding it to the tank. I’ve done that for 4 days and still next to no difference.

    I have live plants In the tank, A plant growing on drift wood. All things that should lower pH. What am I doing wrong?

    1. avatar

      Hey Melanie. I think, you should not focus too much on pH. Guppies are very adaptive and if they are used to a certain pH level, they will do just fine. The best is to keep the pH level between 7 and 8, but most important is to keep it stable.

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