pH Level & Algae Treatment

I often get complaints from clients with green, “pea soup” water in their ponds and even when they apply various algae treatments, the water might clear up a bit to often return to a worse case scenario than what they initially experienced.

It is very difficult to guess the exact circumstance of each aquatic ecology in different water bodies but years of experience in the industry has proved that green water control is related to your water pH, which is related to carbon hardness (KH).

Therefore it is important to regulate your pond’s pH level in order for ANY treatment to offer desired results. fluctuate daily and is determined by complex relationships between carbon dioxide, hardness, alkalinity, photosynthesis, and respiration

Regularly monitor the pH levels

pH levels fluctuates frequently and are also related to complex relationships between carbon dioxide, hardness, alkalinity, photosynthesis, respiration and pollution. pH can also be effected by other factors such as rain, thunder, an accumulation of biological waste, direct sunlight, in some cases fish food, chemical water treatment products and if you are using borehole water, most likely the water calcium or lime levels.

Check the pH levels in your pond during Spring, Summer or even rainfall season every 2 to 3 days. Do not test it with pH strips, instead invest in a good pH water tester. Talk to your Pet Store assistant or take a look at these online options. As you will need to measure pH regularly either taking it to your nearest Pet store for testing or investing in a meter that is accurate and reliable is of utmost importance. A balance pH is the foundation of a healthy balanced water ecology that will make treating algae so much more effective with any water treatment and preserve the water clarity for much longer.

What should my pH reading be?

For algae and green water control we recommend maintaining a pH balance between 6.8 and 7.2. Some experts say that it can even go up to 7.5 but for me personally, I recommend the 6.8 – 7.2 range to all of my clients as I have found that 7.5 does not offer enough leeway should you want to treat for algae or green water.

When your pH level is too low (below 6.5) the water will become more acidic and can be unhealthy for various aquatic species that can result in sickness and fatalities and impact the water clarity. Beneficial bacteria will also die off in acidic levels and reduce the effectiveness of biological filtration.

A pH level too high will result in more alkaline water which often wrecks havoc in managing the water clarity and often results in green water and algae growth. As mentioned above the ideal level should read between 6.8 and 7.2. An indication of “hard water” is when the pH level is above 7.5 and can indicate that the water contains too much calcium and/or magnesium.

When should I test my pH level

As temperature fluctuates the pH level, it is important to test at the same time periodically. In the morning the pH reading will most likely be lower than in the late afternoon. If possible try and test midday. Alternatively test in the morning and afternoon for up to 3 consecutive days to get an average reading.

What is a pH crash?

This is when your pH level spikes or drops radically over night due to reduced carbon hardness (KH) and can be caused due to heavy rain, pollution and result in either hard or soft water. This can also occur after a water changes when the source water contains reduced KH and therefore it is important to not only test your pond pH levels but also the pH of the source water.

Common signs of a pond pH crash

These results are warning signs of a crashed pH level. Even so, testing is still recommended to measure the accurate pH level reading.

  • Sudden fish fatalities
  • Fish staying at the bottom of the pond
  • Fish gasping for air at the surface
  • Lethargic fish
  • Increase slimy layer on the fish
  • Murky or green water
  • Sudden growth of algae
  • Dying aquatic plants
  • Filter or pond water odour

How to prevent a pH crash

Although it is impossible to prevent the fluctuation of the pH level, you can follow some of these steps to prevent the harmful effect of a pH crash on your fish or aquatic plants.

  1. When doing a filter backwash or adding new water to your pond: First remove the water (do the backwash) then add Organic Aqua GT o.r Water Care into your pond to condition the water, remove chlorine, heavy metals and other contaminants before adding fresh water. Apply GT once every 2 weeks to maintain a natural aquatic water balance.
  2. Add a balanced bacteria to cultivate and prevent the biological waste build up inside your pond. Organic Aqua Filter Activator is an effective natural cultivated bacteria that naturally reduces the waste and ensures more effective filtration. You only need to apply Filter Activator initially and then reapply when more than 50% water has been removed. If you don’t change a lot of water and concentrate only on top ups then reapply once every 6 -12 months.
  3. Stabilise the micro and macro minerals in your water: Organic Aqua Fish Care should be applied once every 4 months to stabilise the micro and macro minerals and to also increase your fish immunity and aquatic plant health.

How to treat green water or algae

  1. STOP CHANGING WATER and reduce your filter backwashing (once a week only if the water is very green)
  2. Balance the pH level between 6.8 & 7.5
  3. Add Photosynthetic bacteria to radically reduce the biological waste and sludge in your pond: Apply the Organic Aqua Pond SludgeBuster. (If you don’t have much visible waste, please note that the algae particles causing green water will die off when you treat them and can result in increasing waste that needs to be removed to clear up your pond.) Apply a double dosage once every 2 weeks for severe algae treatment and once off for murky or green water.
  4. Treat the algae and increase the dissolved oxygen levels. Organic Aqua Pond Algae Treatment naturally increased the dissolved oxygen levels and release beneficial water soluble oils that will starve the algae from its “food” and cause them to die off. Apply once weekly for server algae treatment and once every 2nd week for murky or green water. Repeat until the algae has died off and the pond is clearing

Once the algae has died off and the water is clearing maintain this ecological aquatic balance with:

  1. Perform regular pH level checks
  2. Reduce the inflow of fresh water or change water and perform filter back washing only once weekly and if possible, once bi-weekly (especially during cooler temperatures)
  3. Apply GT or Water Care every time you add fresh water (backwash or removing water)
  4. Apply Pond Oxy Aqua every 2nd week or directly after heavy rains, thunder or an extremely hot day, to maintain increased dissolved oxygen levels and the healthy aquatic ecology.
  5. Apply Pond Fish Care and Filter Activator once every 4 months.

How to naturally reduce the pH level

There are various products on the market that can assist with balancing the pH level. Depending on the source water pH level, this can become a rather expensive exercise. I found the following methods to be natural and economic options:

  • Vinegar – this is a short term solution and can be applied if the source water pH is neutral (6.5 – 7.2) and the pH changed due to temporary factors such as heavy rainfall or an extreme hot day.
  • Peat Moss – this is more long term and recommended for hard water where the source water has got a pH level of above 7.5. How to treat with Peat Moss, add it into your filter or allow to float in a plastic net in your pond. Do not exceed 150 to 200 milligrams per litre


This is a short term solution and often used in smaller bodies of water or aquariums.
• Add standard, white household vinegar to your pond if the pH testing kit
reveals a pH that’s above 7.5. Use 1/4 cup of vinegar for every 2000L of
water in your pond. The acid in the vinegar helps neutralise the alkalinity
and lower the pond water’s pH levels.
• Wait for 12 hours, then retest the pond water. If the pH is still above 7.5,
repeat the vinegar application and continue until the pH measures at 7.5
or lower.

Peat Moss

This is recommended as a long term solution, especially where the source water has got a pH reading above 7.5 Peat moss will soften your pond water by binding the calcium and magnesium ions while simultaneously releasing tannic and gallic acids into the water. These acids then attack the bicarbonates in the water, reducing the water’s carbonate hardness and pH. Although there is no exact application recommendation, you can follow the suggestion below and regular testing will show if you need to add more Peat Moss.

  • Water capacity litters / 20 = the amount of Peat Moss. So for 1000L of water you should apply 500g of Peat moss.
  • Add it directly to your filter (wrap it in filter media such as the old school “filter floss” and then place it inside your filter).
  • Some of my clients have had great success by adding the peat moss into plastic net bags (like the ones you buy your onions or oranges in) and allowing it to float directly in the pond water or tying it underneath the water inflow or a waterfall feature.

How to naturally increase the pH level

This is achieved by either applying:

  • Bicarb – this is once again a short term solution
  • Crushed Coral or oyster shells, dolomite or limestone – this is a long term solution where the source water is too soft.
  • Dolomite or Limestone


1 teaspoon for every 35L of pond water. (250grams / 8 000L pond)
• Best practice is to collect some pond water in a bucket and dissolve the
in the bucket. Then pour the entire contents directly into the pond water. Be sure to rinse out any bicarb that remains on the bottom of the bucket.

Crushed Coral or Oyster Shells

Similar to the Peat Moss it is a bitt of a guessing game getting the right application dosage for Crushed coral or Oyster shells.

  • Water capacity litters / 20 = the amount of crushed shells. So for 1000L of water you should apply 500g.
  • Add it directly to your filter with the gravel

I love to hear from you!

Let me know what works for you to balance the pH levels in the comments below. Happy organic fish keeping!


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