Interesting PH Observation

[pecan]

The first year of our pond the ph was consistently at about 9.0. Second year it was consistently at about 8.5, last year 8.0 and this year 7.5.

I have done nothing to change the ph. Except the fist year adding white vinegar every few days until I got tired of doing it. I thought high ph was better than moving the ph too much so I left it alone.

I wonder if that is typical for a pond as it ages.

Maybe it is the rocks that surround the pond initially leaching more minerals raising the ph and each year as they have been in the pond longer the ph isn't impacted as much by them.

 

[koiguy1969]

a stable ph is important. ph swings are the real ph health issue.

 

[DoDad]

My pH is 8.2 and I never worry about it even after a hard rainy period. Low pH and lots of rain are a problem.

 

[Mmathis]

That is interesting.

 

[crsublette]

The first year of our pond the ph was consistently at about 9.0. Second year it was consistently at about 8.5, last year 8.0 and this year 7.5.

I have done nothing to change the ph. Except the fist year adding white vinegar every few days until I got tired of doing it. I thought high ph was better than moving the ph too much so I left it alone.

I wonder if that is typical for a pond as it ages.

Maybe it is the rocks that surround the pond initially leaching more minerals raising the ph and each year as they have been in the pond longer the ph isn't impacted as much by them.

Short answer....

What's been your alkalinity (KH value) through out the period of time and do you primarily use complex calcium carbonate products (i.e., oyster shells, coral, aragonite, etc) ?

Essentially, your pond and critters are maturing. I imagine your fish were smaller and ate less food back during the first year and last year and also I imagine your plants have a better root system now. So, I imagine there is more production and consumption of total ammonia and both of these actions consumes your alkalinity thus allowing your pH to become lower..

Also, as a pond matures, microorganism colonies mature and become more efficient at processing at a lower pH.

My guess is that you are primarily using a complex calcium carbonate product (i.e., oyster shells or coral or aragonite, etc), or some other leaching is involved from stone or other materials, and your pond is reaching its pH equilibrium. pH equilibrium occurs when the consumers and producers come to an "agreement".

This "agreement" will be disrupted once the consumers, such as alkalinity or products releasing alkalinity, starts to decrease, which means either you need to add more complex calcium carbonate products or, depending on how fast your alkalinity falls, then will need to use baking soda (sodium bicarbonate) or gardening potash (potassium carbonate). The potash product is talked about in post#23 of Raising KH with coral or oyster thread.

Your pond's pH was likely initially high due to the lack of calcium due to leaching, or creation, of carbonates from rocks or other materials/processes into the pond causing the pH to initially be high.


Geeky answer...

KH is one major determining variable in the pH.

In most pond waters, the bicarbonate/carbonate buffer system is most dominant due to most waters encounter various forms of limestone or other complex calcium carbonate rock formations and carbon dioxide. Carbon dioxide is one major actor in creating the bicarbonate/carbonate buffer system since algae, microorganisms, the air, fish, and plants are constantly creating and consuming carbon dioxide.

Three major water equilibria's of the bicarbonate/carbonate buffer system is, as described by the henderson-hasselbalch equation ( pH = pKa + log([HCO3-]/[H2CO3]) ) and bicarbonate/carbonate equilibriums below:

H2O <-> H+ + OH- ([H+][OH-] = 10^-14)
H2CO3 <-> H+ + HCO3- ([H+][HCO3-]/[H2CO3] = 4.16 x 10^-7)
HCO3- <-> H+ + CO3-- ([H+][CO3--]/[HCO3-] = 4.84 x 10^-11)

HCO3- is bicarbonate and CO32- (CO3--) is carbonate.

KH is the approximate measurement of bicarbonate.

H2CO3 is carbonic acid, which is what is created when carbon dioxide (CO2) dissolves into water (H2O), which is a relatively slow process.

Takes a combination of an acid, such as carbonic acid (H2CO3), and its accompanying salts (HCO3- or CO32-) to create a buffer system.

There is no good measurement of carbonate for hobbyists so we mainly pay attention to pH to try to assume the free calcium concentrations unless a calcium test is used and everyone's required level of free calcium is different. Free calcium neutralizes carbonate (CO32-) by precipitating to create calcium carbonate (CaCO3), which starts to dissolve again when the pH drops below 8.2.

To better understand the bicarbonate/carbonate pH buffer system, then do a google image search for " freshwater carbonate speciation bjerrum plot " or click here for the search results.

 

[crsublette]

My pH is 8.2 and I never worry about it even after a hard rainy period. Low pH and lots of rain are a problem.

Generally it is true for most ponds, that is "low pH and lots of rain being a problem", since most pond water is dominant in the bicarbonate/carbonate buffer system.

There are the uncommon situations where the pond's source water is tremendously more dominant in phosphates and this changes the pH system due to the phosphate buffering system. Phosphate dominant waters mostly occur in areas where there is a significant presence of phosphate mines and underground aquifers lined with phosphate rock formations. When this occurs, then it is common with this type of buffer system to have a stable pH at around 7.5 while having a crazy high alkalinity. An easy way to know this is if your source water instantly jumps high on a phosphate test. This is more common to occur in area around North Carolina due to the presence of very heavy phosphate rock deposits; however, often times, local water municipalities filter out this excess phosphate. In our context, this is the only moment when the pond phosphate test kits are useful; in other words, if the source water's phosphate reading is crazy, that is off the charts, then this means your water will likely be dominant in the phosphate buffering system.

So, it is the low alkalinity concentrations, rather than low pH, that allows very heavy rains to cause pH problems.

 

[dieselplower]

Out of curiosity if I have a 1600 gallon pond with a surface area of 9'x8' and no way for runoff water to enter the pond, would I really have to worry about a lot of rain lowering the ph too much or whatever it does? I mean even if we got 6" of rain, some would mix in and some would overflow out but with 1600 gallons it couldnt be a significant enough amount to worry about?

 

[crsublette]

Out of curiosity if I have a 1600 gallon pond with a surface area of 9'x8' and no way for runoff water to enter the pond, would I really have to worry about a lot of rain lowering the ph too much or whatever it does? I mean even if we got 6" of rain, some would mix in and some would overflow out but with 1600 gallons it couldnt be a significant enough amount to worry about?

Good catch, which leads me to clarify my previous post...

To be more precise, for rain to have an impact on pH, It depends on your alkalinity concentrations and the volume of your pond...

To try to explain my experience, along with addy's experience, here is an interesting thread... rain/ pollen/ wind/spring water test results

Due to my low volume of water with a crazy high KH value and addy's pond low KH except huge volume of water, then it takes a quite significant amount of rain to impact the pH for both of us.

Remember, ppm is only a volume concentration measurement, which KH is measured in ppm's. For example, if there is a 8 dKH (or 143ppm) measurement for both a 500 gallon pond and a 1500 gallon pond, then this means the 1500 gallon pond actually has 3 times more alkalinity, or KH, when compared to a 500 gallon pond. So, 6 inches of rain impacts a 500 gallon pond much more then it will ever impact a 1500 gallon pond.

So, there is much to take into consideration. and makes it tough to give a direct answer.

 

[pecan]

I don't use any "complex calcium carbonate product (i.e., oyster shells or coral or aragonite, etc)", never have.

Here in the high desert everything has a high ph. Soil is around 8.0 - 8.5 naturally. My tap water is about 7.5-8.0. We only get 10" a rain fall a year so rain is not a concern as far as lowering the ph of anything. I learned in college how climate impacts soil and found it very interesting. But to tell it short, places with lots of rain have lower ph than places with little rain and the Sierra Nevada mountains stop most moisture from getting to the great basin which is just a really big high desert.

I have never tested kh.

But I think the pond is finding a natural balance this year. I heard some where it takes about 3 years for ponds to mature to a natural balance. I also heard that this is when you really see if the entire design, fish load, filtration can work together in harmony or not.

 

[crsublette]

1) I don't use any "complex calcium carbonate product (i.e., oyster shells or coral or aragonite, etc)", never have. Here in the high desert everything has a high ph. Soil is around 8.0 - 8.5 naturally. My tap water is about 7.5-8.0. We only get 10" a rain fall a year so rain is not a concern as far as lowering the ph of anything.

Your soil and water is essentially "acting like" the complex calcium carbonate products.

I am in the same climate, that is the semi-arid desert area of the high plains, annually averaging 3~8" precipitation (depending where you are), and volatile / low humidity where there is a significant evaporation rate along with constant quite high winds. Our soil is around 7.8 pH with a groundwater of 8.4 pH along with a high alkalinity so, back when I was using this water, I never had to use any type of carbonate products and my pond stayed at 8.0~8.2.

The water "top offs" to replace the water that evaporated is what kept the water stable, which is what was essentially "acting like" a calcium carbonate product (except without the calcium) and this is what allowed everything to come into balance.

So, I bet, more than anything, the surrounding soil, climate, source water chemistry, number of fish and level of biological activity, and amongst other variables is what is helping your pond maintain an equilibrium


2) I learned in college how climate impacts soil and found it very interesting. But to tell it short, places with lots of rain have lower ph than places with little rain

Makes sense. Rain is incredibly acidic and void of a noticeable alkalinity. So, in areas with high precipitation, then the soil's chemistry would show change due to the rain's low alkalinity.


3) I have never tested kh.

The entire reason for the "geeky answer" was to explain how a depleted KH is what allows a pH to lower and harmful pH swings only happen due to a depleted KH, a reduction in carbonate production inputs, significant algae blooms, and an increase in biological activity, such as higher feedings and more fish, can speed up this process. So.... it's something to think about.

If your pH continues to stays relatively stable without the need of any products nor testing, then no worries.


4) But I think the pond is finding a natural balance this year. I heard some where it takes about 3 years for ponds to mature to a natural balance. I also heard that this is when you really see if the entire design, fish load, filtration can work together in harmony or not.

Yep, I agree for the most part, which is talked about in post#14 of thread Pond Cycle?.

Everything you're experiencing makes sense to me.

Hope everything continues to go well.

1) I don't use any "complex calcium carbonate product (i.e., oyster shells or coral or aragonite, etc)", never have.
Here in the high desert everything has a high ph. Soil is around 8.0 - 8.5 naturally. My tap water is about 7.5-8.0. We only get 10" a rain fall a year so rain is not a concern as far as lowering the ph of anything. 2) I learned in college how climate impacts soil and found it very interesting. But to tell it short, places with lots of rain have lower ph than places with little rain and the Sierra Nevada mountains stop most moisture from getting to the great basin which is just a really big high desert.

3) I have never tested kh.

4) But I think the pond is finding a natural balance this year. I heard some where it takes about 3 years for ponds to mature to a natural balance. I also heard that this is when you really see if the entire design, fish load, filtration can work together in harmony or not.

 

[crsublette]

Out of curiosity if I have a 1600 gallon pond with a surface area of 9'x8' and no way for runoff water to enter the pond, would I really have to worry about a lot of rain lowering the ph too much or whatever it does? I mean even if we got 6" of rain, some would mix in and some would overflow out but with 1600 gallons it couldnt be a significant enough amount to worry about?

After some thinking on this... You could do a little experiment with some rain water and pond water to help you determine the coefficient of alkalinity depletion due to the rain matching 100% of the pond water. Once you know this coefficient, then you would simply multiply it by your pond water's alkalinity then multiply it by the rain to pond dilution rate. Now, this will not take into account of all the other "stuff" that is in your pond reducing alkalinity consumption, but this would give you the worst case scenario.


So, after some thinking, I would approach the experiment like this...

1. Be sure the rain capture container is cleaned quite well by hydrogen peroxide or distilled water. Personally, I would use deionized reverse osmosis water since it is a better solvent, that is if you have access to it. The reason for this is that rain water is quite acidic and is a solvent; so, when at the moment of capture, it will instantly dissolve any residue that is in the capture container thus changing the rain's alkalinity and pH.

2. Obtain 8 ounces of rain water using the cleaned capture container and test the rain's alkalinity, that is KH value. Try not to agitate it too much just yet so you get a good KH value.

3. Obtain 8 ounces of pond water and test the pond water's alkalinity, that is KH value.

4. Mix these two liquids, stir aggressively for a few minutes to remove as much of the carbon dioxide out of the rain water as possible, then leave it alone for a hour or less to make sure the alkalinity properly equillibriates.

5. Test the solution's alkalinity, that is KH value.

Now, this new KH value is essentially what your pond's KH value would theoretically be without the extra "stuff" that is in your pond when diluting your pond volume with 100% of the equivalent volume with rain water. Lets call this coefficient the "rainKhDepletionCoefficient"

Now, determine how much the pond was diluted with rain water.

pondDilution = Rain inches in gallons divided by pond volume.

To determine rain inches in gallons, essentially, determine your pond's surface area and multiply it by .623, which is the coefficient for the number of gallons per. sq. foot of surface area per 1 inch of rain, and then multiply this by the inches of rain. For example, if pond surface area is 10x13 sq feet, which is 130 total sq. feet ; multiply 130 x .623 = 80.99 gallons due to 1 inch of rain ; then multiply 80.99 by the total of rain inches received. So, if you only receive 4 inches of rain, then 4 x 80.99 = 323.96 gallons due to 4 inches of rain falling directly on the surface water.... Now, for rain off, then guess approximately on the surface area that is dumping rain in to the pond and go from there.


In other words, the above would have an equation syntax of....

( rainKhDepletionCoefficient * pondDilution * pondKH ) = KH depletion due to X amount of rain ...this would be a worst case scenario since it does not include the other "stuff" that could slow down the KH depletion


I would have to think more about it and do a few experiments to tweak it, but it is a starting point.

 

[Waterbug]

Out of curiosity if I have a 1600 gallon pond with a surface area of 9'x8' and no way for runoff water to enter the pond, would I really have to worry about a lot of rain lowering the ph too much or whatever it does? I mean even if we got 6" of rain, some would mix in and some would overflow out but with 1600 gallons it couldnt be a significant enough amount to worry about?

Depends on your KH level. 6" of rain from say a thunderstorm could be down in the 2.5 pH range. Normal rain in your area is about 4.5 pH. Even if rain water stayed on the surface and overflowed out it (not likely) it could still pull KH out of the pond. These things spread out in the water, like O2 does in air.

 

[pecan]

I have been meaning to get a KH tester. But have not found any at local pond shops. I have to order it online. And you know how it is, you don't think about it when things are fine, then when you actually need it you don't have it. LOL

There is a local pond guy who opened a small shop as part of research for his masters degree. He mentioned out here because of our unusually high number of sunny days we have to deal with more evaporation than most places and when the water evaporates, it leaves behind the minerals. He invented something he calls water sweetener specifically for ponds in our climate. Not sure what it is and I don't know any more about it than that but find the theory interesting.

 

[Waterbug]

It is so sad to read that kind of scam. Unfortunately it is so common by people selling pond stuff.

I don't know what this magic "water sweetener" is but "sweetening" refers to making it more alkaline. Evaporation makes water more alkaline so he's making water even more alkaline?

His con would be a bit better if he just said what really happens in most ponds. Because of the large load of decay and waste ponds generate they tend to become less alkaline. Decay and waste conversion produces acid making water more "sour". It is very common, and has been for many years, for pond owners to "sweeten" water on a regular basis. We normally say increasing KH but also GH sometimes. The most popular water sweetener is baking soda. But more expensive carbonates can be used. I doubt this dude has found a new chemical. More likely he sells cheap baking soda as expensive water sweetener.

I assume his masters is in marketing because his back story is so poor. Or maybe it's just that people have heard the word "evaporation" and that's good enough to trick people. If you say a bunch of words people don't understand their eyes glass over and they don't buy. Say a few sciency sounding words people have heard before and the story sounds good.

 

[pecan]

Interesting WB, thanks for explaining. Knowing this guy I don't doubt what you say at all.