# More KH questions



## Bryeman (Aug 24, 2009)

I currently have a 125g tank with CO2 injection, good water movement, good lighting, etc. The KH is between 1.5 and 2.00. I'm not having any problems with my tank, but I currently have the pH down to 6.1 to 6.2 consistently. I'm worried that I'll not be able to put shrimp in my tank with any hope of success down the road with a pH so low. I guess the questions I have would be:

1. Would a pH in the 6.0-6.2 range work for Shrimp (Red Cherry, maybe some other algae eating ones)?

2. Does a KH of closer to 4 do anything for the plants really? Does a KH increase of going from let's say 2 to 4 do anything to bring more CO2 consistency? I realize CO2 is based off of the pH/KH relationship, but I was wondering if higher KH meant better distribution? I apologize in advance because this question is probably dumb, but had to ask it.

3. If, based off of the comments here and more research, I decided to raise my KH to 3 or 4 would I just add a certain amount of baking soda per week and be done with it (after water changes) or does the effects of baking soda wear off in a tank during a week's time. Example, let's say I raise it to 4 right away but by week's end could it drop down to 3?


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## timwag2001 (Apr 15, 2009)

1 - the ph change due to co2 does not affect the tds in the water so the ph has no affect on fish or shrimp. too much co2 is bad though.

2- dont fight your water, deal with what you have. dont mess with the kh

3- dont fight your water, deal with what you have. dont mess with the kh


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## tug (Jul 23, 2009)

RCS breed and thrive, even at a pH of 6-6.2. I started with three young ones and they are all over the place. It is the KH, (not pH) that has an effect on critters. While I have 3 dKH, a little higher then yours, RCS should be fine in your tank. No reason to alter your KH.


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## Bryeman (Aug 24, 2009)

Ok, thanks for the replies. I won't change a thing then!


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## HeyPK (Jan 23, 2004)

The pH can have a negative effect on critters if it gets too low. I don't think that 6.0-6.2 will be harmful, however. 

KH is a measure of buffering capacity. The higher the KH, the more acid or base it takes to change the pH a given amount. Basically, water with a higher KH will hold a greater content of CO2 than water with a lower KH. 

If you had pure, distilled water (KH = 0) only a little CO2 would bring the pH down to 6. The higher the KH, the greater the amount of dissolved CO2 that will be necessary to bring the pH down to 6. 

Increasing the KH by adding sodium bicarbonate should be permanent. The sodium bicarbonate does not break down or go away unless it is removed by water changes.


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## tug (Jul 23, 2009)

I should clarify my point for HeyPK. If pH drops below 5, bacteria levels decrease to a point that wastes cannot be broken down and most fish will not survive, but fish are tolerant of wide fluctuation in pH. That is why adding CO2 which drops the pH is not a problem for fish. Not so if you change your KH and it starts to bounce around.

KH has nothing to do with needing more CO2 to bring the pH down, nor does a higher KH hold a greater content of CO2 than water with a lower KH. That is a common misunderstanding of the pH/KH chart for determining levels of CO2. It takes the same CO2 amount/rate to dissolve 30ppm into a KH of say 2.5 as 10. The pH is different (6.4 for a KH of 2.5 and 7.0 for a KH of 10), but the total amount of CO2 is still the same in both cases. http://www.aquarticles.com/articles/..._PH_Chart.html


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## HeyPK (Jan 23, 2004)

On the contrary, KH has a lot to do with needing more CO2 to bring the pH down. Looking at the chart by Giancarlo Podio at http://www.aquarticles.com/articles/plants/Podio_CO2_KH_PH_Chart.html, it can be seen that when the KH is 0.5, the amount of CO2 increases from 9.3 ppm to 15 ppm, an increase of 5.7 ppm, to lower the pH from 6.2 to 6.0. When the KH is 3.0, the amount of CO2 increases from 56 ppm to 87 ppm, an increase of 31 ppm to lower the pH from 6.2 to 6.0. That is more than five times as much CO2 as was necessary at a KH of 0.5 to lower the pH from 6.2 to 6.0.

Measuring KH is usually done by titrating water with acid until the pH reaches 4.5. Since KH is defined as the amount of bicarbonate and carbonate ions in the water, a KH titration assumes that these two ions are the principal buffering compounds, and that other buffering compounds are negligible. This assumption is usually a safe one for naturally occurring freshwater. If you are going to compare different waters, you should start with them all in equilibrium with air having the same CO2 concentration. This is easily done by having all the water samples in equilibrium with atmospheric air. The chart, below, is a titration of some of the local waters around Jackson, Mississippi, where I live. Deionized water was also titrated for comparison. 0.2N HCl was used in the titration.










As can be seen Tougaloo tap water has a high KH compared to the others. Interestingly, Tougaloo Tap water, which comes from a well, has a GH of 0, meaning essentially no calcium or magnesium. The high KH comes entirely from sodium bicarbonate in this water. For my plants I want a reasonably high KH so that when I add CO2, the water can take up enough of it to keep the plants well supplied for at least a day. Tougaloo tap water does that, but my plants were always getting calcium deficiency, and it was hard to get enough calcium in the water with ground limestone or oyster shells. I decided I would rather get the high KH from calcium and magnesium bicarbonates than from sodium bicarbonate, and so I have switched to using rain water and adding ground limestone to get the KH and GH up at the same time.

By the way, limnologists have shown that in soft water lakes with low KH values, the growth of aquatic plants is limited by lack of CO2, whereas in harder water lakes with higher KH's, CO2 is usually not limiting. See Juday, C. 1942. The summer standing crop of plants and animals in four Wisconsin lakes. Trans. Wis. Acad. Sci. 34: 103-135.


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## Diana K (Dec 20, 2007)

If you decide to alter the KH, then keep track of it. Some plants use carbonates as a source of carbon, but usually only when CO2 is in short supply. 

If the KH is really low because of something in the tank removing it, then that something will continue to remove it when you add carbonates in the form of baking soda. For example, my tap water generally has a KH of around 4-5 degrees. When I add this water to tanks with Soil Master Select substrate the KH drops to 0 degrees, and the pH to 6.0. I add baking soda at the rate of 1 teaspoon per 30 gallons and this brings the KH up to 2 degrees, and the pH up to 6.2. It does not last, though. The substrate keeps removing it. 

In other tanks that do not have SMS I can add baking soda to raise the KH and this is stable. However, these tanks are my Rift Lake tanks, and have coral sand substrate and oyster shell grit in the filter. I add the baking soda when I do a water change so the parameters of the new water match the tanks. I do not see the KH (or pH) rising through the week from the coral sand or oystershell grit. Nor do these drop from any cause. 

Here is a test: Go ahead and add baking soda to the tank. Not more than 1 teaspoon per 30 gallons. This will create a small rise in KH that is OK for the fish. Then monitor it through the week. 
I think either of 2 things will happen:
a) It stays stable. In this case add whatever baking soda you want at water change time, and you probably will not have to do any more about it. 
b) It will keep dropping. So you may have to add some baking soda daily or every other day to hold it steady.


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## Bryeman (Aug 24, 2009)

Diana K said:


> If you decide to alter the KH, then keep track of it. Some plants use carbonates as a source of carbon, but usually only when CO2 is in short supply.
> 
> If the KH is really low because of something in the tank removing it, then that something will continue to remove it when you add carbonates in the form of baking soda. For example, my tap water generally has a KH of around 4-5 degrees. When I add this water to tanks with Soil Master Select substrate the KH drops to 0 degrees, and the pH to 6.0. I add baking soda at the rate of 1 teaspoon per 30 gallons and this brings the KH up to 2 degrees, and the pH up to 6.2. It does not last, though. The substrate keeps removing it.
> 
> ...


Thanks for the reply. Good testing info for sure. I know my KH is stable though. I test it at least once per week, and it's also the same right out of the tap. I just really wanted to know whether there was any scientific benefit to having KH of 4 rather than 1.75-2.00 range.


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## tug (Jul 23, 2009)

HeyPK, if the concern is how much CO2 is needed to make the tank acidic at low vs high KH I can understand your point. If that was the concern, but Bryeman is asking if there is any scientific benefit to having KH of 4 rather than 1.75-2.00 range and you are saying that it will hold more CO2. It takes no more CO2 to reach 30ppm in water with a Kh of 4 as it does with water at 2 dKH. The pH would be different, but as you point out a pH of 6 would not be a problem. Are you saying Bryeman needs to raise the KH of their tank?


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## HeyPK (Jan 23, 2004)

I think, if he is monitoring pH constantly, knows his KH, and is using the table to pick a pH that gives him 30 ppm, then KH does not matter. But, I am not sure. I will try to research this a little more.

Most people just go by their drop checkers which, if they have the same kind of water in them as their tank water, just show the pH of their tank. They all go for green, which is 6.6 (grass green) to 6.4 yellow-green). Interestingly, that always seems to work for them. I never hear of their fish having trouble. My tapwater has a KH of around 9, and my fish (when I was using the tap water) had no trouble when I add CO2 until the pH is 6.6 (water + brom thymol blue is grass green). According to the chart, I would have around 60 ppm CO2, which is in the 'too much' range. If the fish are fine, and they seem to be, then why not? I am starting to wonder how they determine how much CO2 is too much. People with automatic pH checkers that continually monitor the pH of the water probably do the same thing. I wonder how many of them just set the pH they want to maintain without taking into account their KH. 

Finally, I would like to know how the CO2 content in these charts is calculated? Is it all free CO2, or is it also CO2 in carbonic acid and in the bicarbonate ion? I suspect that the amount of free CO2 in the water is the critical value for fish, not the total amount of free and bound CO2.


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## Elohim_Meth (Nov 4, 2007)

HeyPK said:


> Finally, I would like to know how the CO2 content in these charts is calculated? Is it all free CO2, or is it also CO2 in carbonic acid and in the bicarbonate ion? I suspect that the amount of free CO2 in the water is the critical value for fish, not the total amount of free and bound CO2.


I believe it is free CO2 that is taken into account, not all the inorganic carbon in water. 
'CO2 in carbonic acid and in the bicarbonate ion' is, strictly speaking, not CO2 already.


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## HeyPK (Jan 23, 2004)

The CO2 in bicarbonate is partially to mostly available to aquatic plants depending on whether or not they can utilize the bicarbonate directly or only utilize free, dissolved CO2. Since CO2, H2CO3, HCO3-, and even CO3-- are all in equilibrium, pulling out CO2 can convert some of the bicarbonate to CO2 and OH-. Plants that only utilize free CO2 can pull out CO2 until the pH gets to around 9 where free CO2 is negligible. That is as far as they can go, but at that point they have gotten some of the CO2 that was tied up in bicarbonate at lower pH's . Plants that can utilize bicarbonate directly (most plants that only grow submerged) take in the bicarbonate, remove the CO2 and excrete hydroxide ion. These plants can remove nearly all the bicarbonate and get the pH up to around 10.5. At this point, most of the bicarbonate ion is gone and the remaining CO2 is largely in the form of the carbonate ion, and no plants are capable of getting CO2 out of that. The chart, below, comes from Elements of Ecology, by R.L. Smith and T.M. Smith. Note that this chart gives the percentage of total CO2 as the pH changes. As the pH increases due to CO2 removal, the *amount* of Total CO2 decreases. This chart just gives the percent distribution of the *remaining* CO2 in the various forms.


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## tug (Jul 23, 2009)

Hi HeyPK,
Some interesting topics for discussion. You even demonstrate (i think) why most people no longer use the pH of the tank water to regulate the amount of CO2 with pH controllers. There are just too many variables that effect pH. There is no need to check the tank's pH on a regular bases - it is often more misleading then not.

Water from the aquarium/tap is not used in drop checkers for the same reason. All of the write ups about pH/CO2 mention that it is only good if there is no phosphate or other ions in the water that affect its KH or pH, and we dose phosphates, add wood and peat which decrease pH, and who knows what else in the water is affecting the KH or pH readings.

To have a drop checker show a certain ppm of CO2 in water go back to the KH/pH/CO2 tables and equation. Eliminate the reasons the equation and table don't work for aquarium water. To do that, use water that meets the requirements of the equation - no ions that affect the KH or the pH except CO2 and carbonates, (distilled water dosed with sodium bicarbonate often to a KH of 4 dKH). At 30 ppm of CO2, with a pH of 6.6, the KH will be 4 dKH. The following link shows variations on this idea that use more then one drop checker, each set to a different KH for more accuracy. http://wet.biggiantnerds.com/drop_calc.pl

Drop checkers have some inaccuracy inherent to determining subtle color differences and lag time. So, some small adjustments to CO2 based on observations. Still, it is very difficult to get an accurate reading of CO2 in water. If it could only be as easy as some of the tests for nitrite.


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## HeyPK (Jan 23, 2004)

LaMotte has a CO2 kit that uses just a simple titration with a known concentration of sodium hydroxide. You titrate until you get a pink color with phenolphthalein indicator. This procedure assumes that carbonate and bicarbonate are the only meaningful contributors to the KH of your water. But, if other, non-CO2 compounds are contributing, there is a workaround. You titrate two samples, one straight out of the tank, and the other also from the tank, but after it has stood for 24 hours in a shallow dish so that it is in equilibrium with atmospheric air. The difference is a good estimate of 'meaningful' CO2 content because the atmospheric concentration of CO2 is 0.033% which is so low that the CO2 in water which is in equilibrium with the air is on the low side for normal growth in aquatic plants that don't have finely divided, thin leaves, according to G. Evelyn Hutchinson, A treatise on Limnology, Vol. III, pp. 145-146.

So, if you really want to get a meaningful picture of CO2 content, that is the best way I can think of to get it because other compounds that may contribute to KH and falsely inflate the CO2 estimation do not escape into the air as CO2 does.


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## tug (Jul 23, 2009)

According to LaMotte, the most accurate CO2 reading would be with an accurate pH and KH reading. Here's the email from LaMotte as it appeared on the APD.

_______ E-Mail from LaMotte Technical Services ______________________


> The test method for carbon dioxide is an acid/base titration: meaning that a base (sodium hydroxide) is added to the sample until it neutralizes all of the acid in the sample and brings the pH of the sample up to 8.3 (shown by the color change of phenolphthalein). Carbon dioxide in water is an acid, so it is titrated by the base. But, any other acid in the sample will also be titrated by the base, including the humic acid in your sample. Also, any bases already in the sample will affect the titration. Unfortunately, there is no way to accurately calculate out these interferences.
> For this reason the carbon dioxide titration test is considered to be a quick field test method, only.
> 
> The nomographic method is more accurate, if the pH and alkalinity are measured accurately.


Hmmmm, LaMotte CO2 test ($54) vs Drop checker (about $14, each)?
Thankfully, having an accurate CO2 reading isn't important anyway. Keeping CO2 reasonably stable within a range is all that's needed.


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## Diana K (Dec 20, 2007)

Benefits of slightly higher KH:
If the plants or livestock use the bicarbonate then there is a larger reserve. 
With KH at or above about 3 degrees the pH is less liable to change even when something else is added that might try to alter it. The variation from CO2 for example is a lot greater when the KH is very low.


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## tug (Jul 23, 2009)

Diana K; said:


> Benefits of slightly higher KH:
> If the plants or livestock use the bicarbonate then...


 When this reaction happens in a significant way, a white deposit will appear on leaves (calcium carbonate) and even the hardy Elodea will be an algae food.


Diana K; said:


> With KH at or above about 3 degrees the pH is less liable to change even when something else is added that might try to alter it. The variation from CO2 for example is a lot greater when the KH is very low.


 As I hear it, pH will move a full 1 or 2 units in tide pools, shallow planted lakes and ponds every day, or within a few hours for tide pools. The same thing will occur in aquariums (also without issue) as far as effects on pH due to CO2 changes. Adding toxic levels of CO2 will kill the fish, but not due to pH.

I think Bryeman is looking for a soft water, low pH tank. Do amazonian and malaysian rainforests manage over 1KH in most places? Many tanks are similar and they all seam to do just fine;


AaronT said:


> CO2 can't push water below a pH of 5.0. It's only considered a mild acid.
> 
> I'm using Aquasoil with no buffers and my KH is somewhere between 0 and 1 degrees (similar to yours). I'm running CO2 and I have Niger Ottos (they spawned), American flag fish, shrimp and olive nerite snails. All of those fauna are doing quite well despite the extremely low pH.


Nutrient absorption might not apply completely, but the effect of pH on nutrient absorption suggests Bryeman is in a good place with a pH in the 6.0-6.2 range.

Hydroponics: a practical guide for the soilless grower,
http://books.google.com/books?id=3u...result&resnum=4&ct=result#v=onepage&q&f=false


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## Bryeman (Aug 24, 2009)

I'm going to leave my KH alone for now. It's 1.75-2.00 and everything seems to be going as well as possible for a tank startup, especially considering I didn't have enough plants when I started. My plants are doing well and my pH is pretty stable. I have 2 drop checkers and everything seems dialed in or close to it. I'm still trying to dial in the flow, but I think I'm going to go with current set up of about 1000gph movement and see what happens for a while. Thanks to all who commented so far on these questions of mine. Very interesting stuff (to me anyway)!


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