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pH Stabiliser


Dr. Eric Johnson, in his book Koi Health and Disease, describe various ways to raise pH in a pond. The most remarkable piece of advice to prevent pH problems from occurring is the use of the “pH pill”. Although the book describes the use of the pH pill in fish tanks, I have used it now for considerable time successfully in all my ponds. Over time I have improved the concept to some extent and am happy to share the method used with readers.

Basically the pH pill or pH Stabiliser is placed in a filter or in any area with considerable water flow in a pond. The Stabiliser will dissolve over time when there is a fluctuation in the pH of the pond. Established ponds will normally maintain their equilibrium pH value if sludge and decaying organic material is routinely removed from the pond by backwashing the mechanical filter, and biological converter.  Scheduled water changes (10% per week for a small pond, less for larger ponds) are also helpful if the pH of the source water is high enough.

pH can be very, very dynamic. The pH can change overnight. In particular, the pH is prone to fall, and "crashes" are quick, and fatal. Interestingly, many people say they checked the pH last week, and are surprised to find that the pH can change overnight. In simple terms, the pH is supported in range by the carbonate activity of the water and when the carbonates are exhausted, or overloaded, the pH plummets to 5.5 and kills filter bacteria and fish. In other situations, the pH can glide downward very slowly over months and thus your resident fish can survive a low pH but the new fish you keep buying perish quickly as they enter the water with a very acid pH.

The concept of the pH Stabilizer is fairly simple. The calcium carbonate in this product will prevent the pH from dropping to dangerous levels. It is also enriched with more than 60 easily assimilated minerals including vital trace elements. Just place it in the filter and it will dissolve when there is a drop in the pH level.

The Stabiliser that I have used successfully consists of the following.

1. Four parts high grade Plaster of Paris. Ensure that it does not contain any other substance, for instance hardeners, etc.

2. One part Montmorillonite Clay

Plaster of Paris consists of limestone and gypsum. Limestone is made up of Calcium and Magnesium Carbonate, while Montmorillonite clay consists of essential minerals and trace elements. The benefits of the combination of Plaster of Paris and Montmorillonite Clay are to increase the “buffer” effect of the water against pH crashes and also to release the minerals and trace elements into the water. More information about the benefits of Montmorillonite clay can be found here.

In short, the use of clay will improve the lustre and colours of the fish, enhance the water clarity of the pond and boost the bacterial colonies in the biological filter.

How to go about it.

Prepare the following:

1. One bucket for mixing.

2. Smaller flexible plastic containers of your choice for setting. I kg margarine/ice cream tubs work well. Spray the containers with Spray and Cook on the inside!

3. Mix the four parts Plaster of Paris and one part Montmorillonite Clay in the bucket while still in a dry form. The reason for pre-mixing the dry parts is to prevent the clay from forming lumps when you add water. Add tap water to the mixture and stir well. When no lumps are left, pour the contents of the bucket into the smaller prepared containers. You have to work reasonably fast because the Plaster of Paris sets within a few minutes. Leave for a few hours to harden completely and then remove it from the flexible containers. Store the “pH Pill” or pH Stabiliser in a well ventilated area to dry completely. When dry, the Stabiliser should be lightweight and to the touch it will resemble black board chalk.

4. Once it is completely dry one can place the pH stabiliser in the filter or as said in a place where there is a constant flow of water over the pH stabiliser.


I have noted the following when I use the pH stabiliser:

1. The pH stabiliser will slowly dissolve in a pond with a pH between 7.5 and 8.0.

2. When the pH of the water is below 7.0 it is advisable to add a few cups of Bicarbonate of soda (Baking Soda) to the water to assist the pH stabiliser to keep the pH stable and to prevent the stabiliser from dissolving too quickly. Alternatively one can replace the Stabiliser after a week with another block.

3. When I have added up to three pH Stabiliser blocks to a pond, the pH never rose higher than 8.1. The conclusion that I came to is that especially in a big pond, it will be completely safe to add three or more blocks measuring 15 x 15 x 15 cm.

4. Within the first few days after adding the pH Stabiliser, a lot of suspended solids in the pond would accumulate in the settlement chamber of the filter, improving the water clarity. This can be flusher away easily.

5. The minerals will also be released slowly to benefit the fish as well as the beneficial bacteria.


Dr. Johnson, in the abovementioned book, also suggested that it may be an excellent way to introduce some medication into ponds because of the slow dissolving nature of the pH Stabiliser. I am experimenting with this idea, but face numerous uncontrollable factors such as the rate that the Stabiliser will dissolve in different ponds, the stability of the active ingredient in medication when in contact with water and the uncertainty whether chemicals will leach out of the Stabiliser, much faster than the actual time it takes the Stabiliser to dissolve.

Last Updated on Wednesday, 29 February 2012 12:53