A selection of articles

Acidification - Revisited

All of you who are heavily feeding your fish will know the problem of acidification of your pond. Also called "acid creep", when the pH drops so low that it affects the appetite of your priced collection and rendering the biological filtration virtually non-effective. You might even find white patches developing on their fins and body. The fish normally become lithargic and listless. 

So you jump to the old "bicarb" packet to solve the problem and your battle with "perfect" water starts all over again. Because just when you think you have it right, off it goes again.


That is because keeping perfect water in a koi pond (as Dr Tsai once explained) is like sitting on a samurai sword - no matter what you do, the blade will cut you to size.

The problem with sodium bicarbonate is that it only adds alkalinity to lift the pH. It works of cause, but the biological filter relentlessly continues titrating the alkalinity with the end product of nitrification - nitric acid. Protons (H+) and nitrate (NO3-). So the cycle continues.

You should not confuse the chemistry of swimming pool water with that in your koi pond. In pools you are adding hardness indirectly by way of the calcium ions in the “chlorine” you so readily add. That improves the buffering. The calcium hypochlorite or HTH together with the “bicarb” sorts out your pH requirement for effective sterilization with chlorine. 

When pH gets too low, the alkalinity is gone, then the pond cement presents itself as a source of alkalinity. Ever seen how a “naked” concrete gets pitted below the waterline over time? If you have a poorly sealed concrete pond or cement waterfall, that then serves to slow down the acid creep by the cement (alkaline) component of the building works. That’s why many poorly built and sealed brick and mortar pond will spring a leak after a few years’ service. That’s why, depending on the sealing product, you need to get the sealing redone after a few years and why it is so important to get it done properly. Only one spot on weakness and the acidic water will get to the plaster and start its damaging work.

But ok,  you have a fiber-glassed pond! Great! So no source of alkalinity from the pond, and it is only you and the bicarb to do battle with the pH. But you know all this, have seen the mountains of oyster shells the Japanese breeders use in their ponds. You also know how difficult is, is to get clean, aged oyster shells. Also note that not all seashells are equally effective. Shells structure is held together with a gelantin-like matrix of organic origin. In most shells it also slowly dissolves into the water increasing the organic load, but is other cases it leaves you with a messy insoluble blob.

StabHi is a limestone rock that contains all the calcium carbonate you need to stabilize the pH fluctuations in the pond water. Very important, it adds alkalinity to the pond, but also adds calcium and magnesium to the water that are essential for water hardness. Not only a component of healthy water but essential for all forms of life in the pond. Even your biological filter will starve without it. That is why you test your pond to have at least 100mg/litre of hardness .

For pond keeper the buffer point of calcium carbonate may not be ideal, but it goes a long way to stabilizing the pH.
The following factors inter alia determine the volume of StabHi to use for your pond to get best results.

1.    Total exposed surface area of the StabHi
2.    The pH differential from the buffer point,
3.    feeding rate
4.    protein content of the food
5.    flow rate over the StabHi
6.    temperature
7.    effectively of the biological filtration
8.    constitution of the top-up water
9.    amount of sunlight in the diurnal cycle the pond gets
10.    volume of top-up over a given time

As you can see that is virtually impossible to make a recommendation. Talk to other people in your area using StabHi. Those with similar feeding regimes. Or else just start with one 4kg bag per 5000 liter pond water. Give it time and don’t expect mediate sharp pH variations. Adjust as you go.

Servaas de Kock
20 August 2013 - Updated 30/6/2017

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