Until last year, I thought I was a pretty competent pond keeper. I was, after all, Mr. Water Quality for my club. Maybe Arrogant Mr. Water Quality would have been more appropriate. Until last winter, I was certain that because I had a gunite pond, I was protected from pH crashes because gunite ponds leach out carbonates that buffer against low pH. Consequently, when my club would send out emails warning people to check their pH before and after large rain storms, I would ignore them. This arrogance cost me dearly as I had a pH crash and lost a lot of fish before I could figure out what was wrong and fix it. So what happens during the dreaded pH crash? The total alkalinity of the pond drops to a point that it can no longer buffer pH. When the pond reaches a pH of 6.5, the nitrification bacteria in the bio-converter, or as some would refer to it, the bio-filter, begin to shut down and ammonia begins to climb.
Ok, so what is pH, really? From the World English Dictionary: “potential of hydrogen; a measure of the acidity or alkalinity of a solution equal to the common logarithm of the reciprocal of the concentration ions in moles per cubic liter of solution. Pure water has a pH of 7, acid solutions have a pH less than 7, and alkaline solutions a pH greater than 7.” Wow, that was a mouthful. I could never stay awake to the end of that in my chemistry classes. Please note in this definition the word alkaline is used. Alkaline and base can be used interchangeably to describe the chemical properties of a substance. It is not the same as total alkalinity. My version of pH is derived from what I found on the Science Buddies website. Please keep in mind that this is as it relates to our koi ponds. In water, some of the water molecules dissociate or split up. After the molecules dissociate, you have hydrogen ions (H+) and hydroxide ions (OH-), in addition to the regular water molecules. In pure water, which is seldom the case, you have equal numbers of hydrogen ions and hydroxide ions; the solution is neither acidic nor basic. So what, really, are acids and bases? Acids donate or give up hydrogen ions. When an acid is dissolved in water, there is a surplus of hydrogen ions and the solution is considered to be acidic. A base is a substance that accepts hydrogen ions. When dissolved in water, a base accepts, or soaks up, hydrogen ions resulting in a solution with a surplus of hydroxide ions. This solution would be considered a basic solution.
So what are the extremes? The strongest acid solution has 100 million million more hydrogen ions than the strongest basic solution. That would be a 1 with fourteen zeroes behind it. Remember that common logarithm of the reciprocal thing? There is no coincidence that the pH scale goes from 0 to 14. It gives us a chance to assign values to substances without any of those fourteen zeroes. For standard solutions and normal atmospheric pressures, we would expect all substances in solution to fall between 0 and 14 on the pH
scale. It is possible in laboratories under artificial conditions to exceed these limits, values less than 0 and greater than 14. On the pH scale, every change of one number is a ten fold change in ions. Every time you move one number on the scale, one of those fourteen zeroes appears or disappears depending on what direction you are moving. At the mid-point of the scale, pure water, at a temperature of 25â—‹C, would hypothetically have a pH of 7 and a hydrogen ion concentration of zero. At pH 0, concentrated sulphuric acid has ten million times as many hydrogen (H+) ions as pure water. At the other end of the scale, pH 14, sodium hydroxide which is a primary ingredient in drain cleaner has one ten millionth as many.
For our ponds, a pH between 7 and 8.5 is desirable. Our koi can become accustomed to levels as low as 6 and as high as 9, but will not thrive at these levels. Also note that at a pH level below 7, the bioconverter will not be working well and ammonia must be dealt with.
Now checking your pH will tell you one of two things: either your pond is ok; or it isn’t. There really is not a middle ground when checking this water parameter. After the problems encountered last winter, I did a little research. I knew from reading Norm Meck’s article on alkalinity, that total alkalinity plays an important part in pH stability. I am now a firm believer that checking and knowing on a month to month or even bi-monthly basis what your total alkalinity is, is far more important than knowing only your pH level. It is very important to know the total alkalinity of both your pond and your source water. Keeping on top of your pond’s total alkalinity levels will enable you to know when a pH crash is about to happen.
So, just what is alkalinity? Please note that there is a difference between a substance or solution being labeled alkaline and what this article refers to as alkalinity or more properly total alkalinity. Additionally, there is a distinct difference between alkalinity and hardness. For our purposes, alkalinity is associated with the carbonate portion of calcium carbonate. Hardness is a measure sometimes used in aquaculture but most commonly used to determine how much detergent to put in the laundry given the parameters of your local water. It specifically deals with divalent ions such as calcium, magnesium and iron.During my research for this article, I found various different definitions for alkalinity. I feel that the following definition is the most appropriate for our needs and is an excerpt from the Student Watershed Research Project from the University of Portland, Oregon and deals specifically with water in lakes and rivers. “Alkalinity is a measure of the capacity of water or any solution to neutralize or buffer acids. This measure of acid neutralizing capacity is important in figuring out how buffered the water is against sudden changes in pH.” Total alkalinity is properly referred to as a measure of milligrams of calcium carbonate (or equivalent) per liter of solution. This measurement also equates to parts per million (ppm).
Carbonate and bicarbonate ions are the primary sources of alkalinity in water. The carbonate ion, (CO3 )2- is the most effective naturally occurring source of alkalinity as each carbonate ion neutralizes two hydrogen ions (H+) which are acids. The bicarbonate ion (HCO3-) is less effective at neutralizing acid as it will only neutralize one hydrogen ion, but will also neutralize one hydroxide ion (OH-), which is a strong base.
One source of alkalinity is calcium carbonate (CaCO3). When water seeps into underground aquifers through layers containing limestone, calcium carbonate (CaCO3), leaches out of the limestone and is dissolved into the water. For our purposes, calcium carbonate is the best source of alkalinity. It can do two things, bolster total alkalinity and raise pH somewhat. When dissolved in water, calcium carbonate produces molecules of calcium, and carbonate ions. The carbonate ion can then react with water molecules for form bicarbonate ions and hydroxide ions which are both negatively charged and will attract and bond with positively charged hydrogen ions, thus absorbing or neutralizing the acidic hydrogen ion.
In areas where water supplies come from rivers and lakes fed by rain and melting snow from the mountains, where the water moves quickly downstream and little time to erode the volcanic mountainsides, the water has virtually no alkalinity from mineral sources.
Here are some typical ranges for various water sources:
Typical surface water 20 to 200ppm CaCO3
Surface water from regions with alkaline soils 100 to 500ppm CaCO3
Ground (well) water 50 to 1000ppm CaCO3
Please note that quite often, there is a great deal of carbon dioxide dissolved in
ground water producing water that has greater amounts of alkalinity but is also
somewhat acidic. Agitation or the use of degassing columns will remove the
Typically, water coming from rivers and lakes in non-alkaline soil areas, which is basically all of the Western United States, will not only be low in total alkalinity but will be slightly acidic as well. The slight acidity is due to the respiration of oxygen consuming organisms in the water. Animals living in the water consume oxygen and produce carbon dioxide. Carbon dioxide is extremely water soluble and produces carbonic acid, which acidifies the water; this will be discussed in more detail a little later. The end result of this is that water utilities in an effort to reduce corrosion will artificially raise the pH of the water and in doing so, impart a small amount of alkalinity to the water. My municipal water comes from the American River and after treatment to raise the pH, still only has a total alkalinity of less than 30ppm. So what I’m trying to say here is the source water for your pond just might be grossly inadequate for protecting your fish.
“Acid rain” is defined as precipitation with a pH of less than 5.6. Acid rain is not a recent phenomenon. It has been around virtually forever as a natural occurrence. Every time there was a volcanic event, large amounts of sulphur compounds were spewed into the atmosphere only to turn into sulphuric acid and return to the ground. The term “acid rain” as we know it, was coined by the Scottish chemist Robert Angus Smith in 1872 in the book Air and Rain: The Beginnings of a Chemical Climatology. This book was the result of a study that began in 1852 when it was noticed that the forests downwind from industrial areas were markedly declining.
As mentioned earlier acid rain can and does have natural origins. The primary cause of “acid rain” or more properly acid deposition, is air pollution from burning fossil fuels. Acids are not directly released into the air, but large amounts of acid precursors are released. These precursors are primarily sulphur oxides (SOx) and nitrogen oxides (NOx). Although great strides in air pollution reduction have been made in the United States, acid deposition remains a problem, particularly in the Northeast primarily due to the density of coal fired industry and weather patterns that concentrate the resulting pollution. Modern day research has shown that acid rain actually has two forms; dry deposition and wet deposition. Dry deposition occurs when acid producing particles (SOx and NOx) bind with atmospheric dust particles and fall to the ground. Later, when there is precipitation, these acid precursors combine with moisture to form acids. Approximately half of the acids in the atmosphere return to earth in this manner. Wet deposition occurs when these acid precursors combine with water in the air and fall to earth in the form of fog, rain, mist or snow. When fossil fuels with sulphur impurities are combusted, the sulphur is oxidized to form sulphur dioxide (SO2). The sulphur dioxide rises into the atmosphere and is again oxidized by atmospheric hydroxyl ions to form sulphur trioxide (SO3) which reacts with moisture in the air to form sulphuric acid (H2SO4). Sulphur dioxide is responsible for nearly 70% of acid deposition. Nitrogen oxides are also formed during fossil fuel combustion in the form of nitric oxide (NO). Nitric oxide is oxidized in the atmosphere to nitrogen dioxide (NO2) which then reacts with hydroxide ions in the atmosphere to form nitric acid (HNO3). Nitrogen oxides account for approximately 30% of acid rain.
If acid rain is a phenomenon particular to the heavily industrialized areas of the country and those areas downwind in the North East, shouldn’t the rest of the country have rain with pH values approximating that of pure water? After all, isn’t rain essentially distilled water with a pH of 7? I’m sorry, but it is not, all rain is acid rain, it’s just a matter of how acidic it is. Researching this article, it was an eye opener to learn that distilled water, exposed to air, will quickly become acidic. “Why is that?”, you ask. Pure, distilled water has no alkalinity, and thus, no ability to buffer or neutralize acids. The carbon dioxide in our air is highly water soluble and combines with water molecules to form carbonic acid. This would explain why normal rain, with a total alkalinity generally of nearly 0mg/liter CaCO3 generally has a pH value of about 5.7, much more acidic than our ponds. If your pond normally has a pH of 7.7, rain at pH 5.7 would be 100 times more acidic than your pond water. That is how the logarithm works as it relates to pH, each change of one whole number on the scale represents a ten fold change. In other words, if the pond was pH 6.7, the rain at 5.7 is ten times more acidic. But just mixing pond water with a pH of 6.7 and rain at 5.7 does not necessarily mean a significant change to the pond pH. If your pond has sufficient total alkalinity, say, a minimum of 100 mg/liter CaCO3 or 100 ppm, the rain will have minimal effect. If the total alkalinity in your pond is very low, a large amount of rain will cause problems.
Also, if you live in an area where your municipal water source has very low total alkalinity, you may need to be vigilant about your total alkalinity levels. For instance, my own source water, at the tap, only has at the most 30 ppm CaCO3 , if I artificially boost my total alkalinity to 100 ppm and then do a water change, I have effectively reduced my total alkalinity in the pond. If my total alkalinity is already low, I may now be placing myself in a dangerous situation.
Who is most at risk? The person most at risk would be someone with a liner pond and water with low carbonate alkalinity. The next risk level would be a person with an older gunite pond with water that has low carbonate alkalinity. A newer gunite pond with low water alkalinity is not so much at risk as the
gunite will leach carbonates into the water for several years. There is a point at which the gunite shell just doesn’t have any more to give. My pond is at that point. I must constantly monitor the total alkalinity levels of my water, as just doing water changes or adding fresh water is not enough. My test kit of choice is the LaMotte 4491DR. It is not the cheapest out there but gives very precise results.
So what does this kit tell you? It tells you that a precipitous drop in pH may be looming. One would say but my pH is fine, what’s to worry? The need for caution is that as total alkalinity is decreasing, it still protects you from big pH changes although your pH might be dropping ever so slightly. When the total alkalinity drops very low, even small additions of acid may produce large changes in pH. Do you need to stay vigilant in dry periods? Yes, very much so if you have moderate to large stocking densities and source water with low alkalinity. Rain or dry deposition of acidic particles is not the only source of acid in your pond. The carbon dioxide produced by the fish and the action of the bio-converter alone is a substantial source of acids. Aeration, either from waterfalls or air stones will reduce carbon dioxide levels, but the bioconverter produces plenty of acid by itself.
In retrospect, my pond was probably well on its way to a pH crash without the rain. But who knows, were those large rain storms the proverbial straw that broke the camel’s back?
How to protect your pond.
Baking soda can be your best friend. It is relatively cheap, easy to apply and most importantly, won’t burn you like some other strong alkali substances used by very experienced people.I get mine at Sam’s Club in 13lb bags. One pound per 1000 gallons of water will give you an increase in total alkalinity of approx 40 to 60 ppm. I have recently started using crushed oyster shell in a 300 micron bag placed in my water fall. The results so far, have been very promising. Since late November, there have been several substantial rainstorms in my area and I have been able to maintain total alkalinity at 150ppm without having to add any baking soda. While the crushed oyster shell provides great stability, it is very slow to dissolve and won’t produce quick results. When you need alkalinity in a hurry, baking soda will always be your best friend. If you are adding large amounts of baking soda to your pond, keep an eye on your pH levels as they will rise.
If you suspect you that you have had a pH crash.
Check all your water parameters. You will need to especially check for ammonia. I would recommend having a salicylate type kit as opposed to a Nessler reagent kit. Using the Salicylate ammonia test kit will give you true results when using an ammonia binder as it will only show ammonia that is free or unbound. The Nessler kit will show false readings because of interaction with the aldehyde components of the ammonia binder. Often the results are weird and not even found on the color chart although in low concentrations of the ammonia binder, they may appear to show ammonia when there is none (bound or not). If you have ammonia present, you need to deal with that first. My preferred ammonia treatment is ChlorAmX in powder or liquid form. Treat the pond at the specified dosage for the amount of ammonia present. At this point, you may add the baking soda to increase the alkalinity and pH. Failing to deal with the ammonia first will harm the fish as the toxicity of ammonia is directly related to the pH of the water. When the total alkalinity and pH have stabilized, the filter should begin to cycle again. All those bacteria that couldn’t do much at the low pH will kick in and rapidly get things back to normal. All water parameters must be monitored, especially ammonia. Additional small doses of ChlorAmX may be needed during this start-up period.
For further reading, Norm Meck of the Koi Club of San Diego, has published an excellent series of Water Quality articles. These can be found on the internet at www.KoiClubSanDiego.org/library
Key Words: Pond, KH, pH, Acid Rain, Alkalinity, Koi