Fish keepers and tropical fish breeders often worry about their aquarium’s pH because requirements vary among species.  This can lead to them frantically dumping in expensive bottled solutions, baking soda, or vinegar. Unfortunately, that usually results in spikes and crashes that will kill your pet fish.  The number one rule of pH adjustment is if the fish can adapt to your natural parameters, leave it alone.

If it is deemed necessary, there are gentle, natural ways to adjust pH, alkalinity and acidity in aquariums.   Once they’re in place, one only has to remember to do smaller, more frequent water changes so as not to cause a large fluctuation.

Natural Ways to Increase or Decrease Aquarium pH

Results will vary depending on your water supply’s buffering capacity, but we’ve found the following natural methods of adjusting aquarium pH to be effective and safe.  However, each aquarium’s chemistry is different so we suggest that you experiment with adjustments on an empty aquarium until the desired parameters are relatively consistent. Be sure to test at the same time of day to avoid inconsistencies due to natural pH fluctuations.

Naturally Lowering pH in AquariumsIndian Almond Leaf (T. catappa) Extract Tea Bags

Many Tetras and Catfish prefer a lower aquarium pH.  It’s more difficult to lower pH because you can’t remove the minerals (dH) or adjust the buffering capacity within the aquarium without the aid of pre-filtration (reverse osmosis or distilled).  The only option is to systematically overwhelm the process.  Adding the following items will increase acidity to a point where only part is bound by buffering (KH), leaving the rest free to lower pH.

  • Driftwood
  • Cactus Wood
  • Leaf Litter – You can add brown leaves such as Catappa (Indian Almond Leaves), oak or banana leaves, or use an extract bag for less mess.
  • Peat Moss – Peat moss with no chemical additives or purchase peat pellets made for aquariums.  If we use peat we prefer the latter because we can count the pellets, making it easier to produce consistent results. A filter bag will contain the mess.
  • CO2 – If you are a plant enthusiast who adds CO2 to your aquarium the pH will be lower.
  • Remove any items from your aquarium that are on the ‘Increase pH’ list.

Naturally Increasing pH (Alkalinity) in Aquariums

Increase Aquarium pH with Limestone
Our male Skiffia francesae (an endangered Goodeid) swims past Texas Holey Rock.

Many Livebearers and Cichlids prefer higher alkalinity.  Our pH is right around neutral and our buffering capacity is nil.  We’ve found that a focus on increasing the buffering capacity / KH is very effective in providing a stable pH increase.  To that end, we use the following items in our aquariums.

  • Texas Holey Rock
  • Tufa Rock
  • Crushed Oyster Shell – In a filter media bag or box filter. The great thing about oyster shell is you can tell when it’s depleted by volume. Use feed grade to avoid impurities.
  • Sea Shells

    Naturally Increase or decrease Freshwater Aquarium pH GH KH
    Buffering box filter with aragonite, coral, oyster shell, seashells & filter floss.
  • Coral or sand with Aragonite – This can be effective but it will deplete.
  • Calcium Montmorillonite Clay – We add a dash with every water change.  It balances alkalinity, adds minerals to the water column, promotes healing, aids plant growth, and keeps the algae away.  Pet-grade can be depleted or contaminated, so we use pure, edible grade only.
  • Provide water movement – Filtration and air stones aid in CO2 exchange and helps dissolve your natural pH-boosters.
  • Water changes – Vacuum substrate.
  • Air circulation – Too much CO2 in the air can lower pH.  Provide adequate air circulation in your home (a slightly opened window is good for you and the fish) and avoid smoking.
  • Remove any items from your aquarium that are on the ‘Lowering pH’ list.

??? Do you have any tricks to naturally decrease or increase pH in aquariums?  Please share them in the comments below.


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18 thoughts on “Increase or Decrease Freshwater Aquarium pH Naturally ©

  1. I guess if I try all of these at once in my excitement I’ll end up with a big mess. 😀 You have a way of writing that makes a reader get excited about the possibilities. Now I need more fish tanks. I ALWAYS need more fish tanks. 😀

  2. There’s an aquarium topic we don’t see enough of. I guess the natural angle hasn’t hit fish tanks yet, or until now anyway. Thanks a lot.

  3. It’s almost time to go out and collect leaves for my tanks. That’s how I add acidity and the price is right.

  4. I have to agree with leaving it alone if at all possible but if you have to adjust the ph absolutely go natural. There are other things that leaves, shells and other natural additions offer to the environment that together makes a more beneficial environment for fish requiring those conditions.

  5. Oooohhhh I LOVE IT when you write about natural fish! Nobody else does and when they do its halfassed or marketing. Thanks again girl!

  6. I have tufa rock in all of my aquariums & sometimes oyster shells in the filter. My mollies like hard water.

  7. Great comments, thank you. Daryl, best of luck! Some Cory’s are difficult to breed in hard water but many of the common species will do so quite easily.

  8. This post was very helpful thanks. I’m trying to breed corydoras in hard water so wish me luck!

  9. I tried baking soda but it was a pain to keep it up. I phased it out when I was planning a vacation. It’s better for the fish to have more minerals in the water than just adding one thing to increase the ph.

  10. I only use peat for breeding but I haven’t tried the pellets. They’d be more convenient with less mess I bet. We used clay in our koi pond at our other house for algae and to heal spawning injuries but I haven’t tried it in my aquariums, good idea.

  11. Some fish look like they’re doing ok in the wrong aquarium environment but they could still be stressed and weakened. If they need minerals I give them minerals.

  12. Awesome answers to a common aquarium problem. I love the buffer box filter idea, I don’t think I’ve ever seen it before.

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