Ca/Alk imbalance vs. pH....

[cwcross]

MDMAquatic. The carbonate, bicarbonate equilibrium in water is very sensitive to CO2 levels. Small increases in ambient CO2 can cause downward presssure on pH. There are hundreds of cases of people who have had this problem in winter. They run thier venturi intake to the skimmer out the window and the problem clears up. I agree that it is the least likely, but is a frequently reported phenomenon. The partial pressure of CO2 is a significant parameter in the equilibrium equations of carbonate/bicarbonate ratios in seawater. How much impact does it have really? Good question?

Sincerely...Collin

 

[MDMAquatic]

I mean i am not saying that there is not ANY impact...but it has to be so small...is it really a problem?? And i have never heard of anyone that i know of running a venturi intake from the outside...i would think you would be more likely to pollute your water by intaking that garbage outside than if you just kept it the way it orginally was intended. Just my opinon.

 

[cwcross]

I mean i am not saying that there is not ANY impact...but it has to be so small...is it really a problem?? And i have never heard of anyone that i know of running a venturi intake from the outside...i would think you would be more likely to pollute your water by intaking that garbage outside than if you just kept it the way it orginally was intended. Just my opinon.

Well, lets think about it. CO2 distributes itself between ambient air and water according to its equilibrium constant. So if we write this in terms of partial pressures we get something like:

p(CO2)water=K*p(CO2)air

this says that the partial pressue of CO2 in water is proportional to the amount in air. If K is near 1 then a 5% change of CO2 in air will lead to a 5% change of CO2 in the water. The CO2 in the water in turn affects carbonate/bicarbonate equilibrium, which then in turn affects pH. If we assume linearity in all these relationships near 1 (a big assumption) then it is reasonable to expect that a 5% change in pCO2 can lead to a 5% change in pH. At a round pH number of 8.5, 5% of this number is 0.4 pH units. So from pH 8.5 to pH 8.1. A significant change in regard to our target range for a small change in CO2 buildup... I have some links regarding more accurate equations if anyone is interested.

Sincerely...Collin

 

[MDMAquatic]

Now based on that when do you think you will EVER get a change of 5% in your breathing air?? Folks Co2 is not put off by furnaces.....Co is, there may be some very small risidual amounts, if anything it would be caused by people being indoors in a very tightly insulated house and it building up because of resperation in humans. Yet i can tell you that i highly doubt that you would EVER get a 5% change!!!!! Oxygen content has to be bewteen 18-22% Approx. And if you are offsetting that by 5%, which by your equation would only make a .4 change in PH you would be becoming very sick, yet where is this Co2 coming from??? And how could it buildup in such quantity in a household to make a significant change in PH??? If you have a problem like that you should not be worrying about the PH of your tank, you better be worrying about your health!!!!! I do not disagree that ambient air changes in Co2 would change it in water also...what i am questioning is why do you all believe that there would be such a change and buildup of Co2 in your house?? and a small change in Co2 buildup Cwcross??? I would say that anything even NEAR a 5% change is more than small, you had better be seeking some proffessional home improvement help.

 

[DonW]

Co2 is a byproduct of burning Propane, natural gas and fossil fuels such as heating oil and coal. In fact if a co2 generator is nothing more than a natural gas fired flame in a metal box.
As far as it sitting on the floor, yes it does do that. but first it is either blown up or down by the furnace blower. It then settles on top of the waters surface. This happens in both the sump and the aquarium.
Yes it does lower PH and this is a common problem.

Don

 

[Cougra]

I have a problem with that equation, mainly with the logic pertaining to the linear scale of pH. How can you assume a linear scale when pH is measured on a logarithmic scale?

 

[NaH2O]

it would be caused by people being indoors in a very tightly insulated house and it building up because of resperation in humans.

While I don't know much about furnaces (other than flooding duct work), I do know the above quote is true. Respiration is a big factor as well. I have a new home, ALL high efficient natural gas appliances, and I notice more of a pH issue when everyone is home on the weekends. Not anything to write home about, but somewhat of a difference. It might not even be that.....it might be simply time to do some needed tank cleaning.

Here is an article: Low pH: Causes and Cures by Randy Holmes-Farley. Below is a quote related to this discussion:

High indoor carbon dioxide levels can also lead to low pH problems in many tanks. Respiration by people and pets, the use of un-vented appliances burning natural gas (e.g., ovens and stoves) and the use of CaCO3/CO2 reactors can lead to high indoor carbon dioxide levels. The level of carbon dioxide can easily be more than twice that of exterior air, and this excess can substantially lower the pH. This problem is especially severe in newer, more airtight homes. It is unlikely to be a problem in homes like mine where the wind can be felt blowing around old window frames.

Perhaps some pH issues are due to numerous factors, and not just one. For instance, a new tank will have lower pH, as would a tank that is dirty/accumulating organics.....add in a small house containing 30 cats (I know I'm exaggerating) and 3 adults - then you probably would have a pH shift.

Anyway - just some more thoughts.

 

[damer]

try adding some white vinegar to your kalk. have a look at ATJ's site

damien

 

[fishman]

My PH monitor is hosed (needs to be calibrted) . The good news is my PH is fine. I tested the water of a fellow refers system and it tested at 7.6. He controles his system with ph monitor/ calcium reactor.

Have you calibrated your pH meter lately? You should calibrate it at low and high pH standards if it can take a two point curve. Elsewise calibrate it near pH 8-8.5.

I doubt the temperature compensation is the cause. I don't think this would account for a 0.5 unit shift as you are describing. Between the two, I would tend to go with the colorimetric test. This sounds like it could be your problem. However, it is still strange that you are precipitating lime in your tank. What is your Ca level and alk level?

 

[cwcross]

Now based on that when do you think you will EVER get a change of 5% in your breathing air?? Folks Co2 is not put off by furnaces.....Co is

wrong!

In a pure combustion reaction, the only products are H20 and CO2. CO only comes from imperfect combustion.

, there may be some very small risidual amounts, if anything it would be caused by people being indoors in a very tightly insulated house and it building up because of resperation in humans. Yet i can tell you that i highly doubt that you would EVER get a 5% change!!!!!

This is also incorrect.

Oxygen content has to be bewteen 18-22% Approx.

Oxygen can be wherever it wants as can any of the gases that make up our atmosphere. It tends to average around this level globally in this century but that's about it.

And if you are offsetting that by 5%, which by your equation would only make a .4 change in PH you would be becoming very sick, yet where is this Co2 coming from??? And how could it buildup in such quantity in a household to make a significant change in PH??? If you have a problem like that you should not be worrying about the PH of your tank, you better be worrying about your health!!!!! I do not disagree that ambient air changes in Co2 would change it in water also...what i am questioning is why do you all believe that there would be such a change and buildup of Co2 in your house?? and a small change in Co2 buildup Cwcross??? I would say that anything even NEAR a 5% change is more than small, you had better be seeking some proffessional home improvement help.

MDM, I currently have about 3 million dollars of combustion tests going on in 3 countries. This is because among other things, my company pays me to be a "fuels and combustion" expert. Three weeks ago I was in the engine room of a celebrity cruise ship "radiance" climbing around the engine room where we have 2 state of the art GE LM-2500 gas turbine engines. Each turbine burns about 80 metric tons/year of marine gas oil or light cycle oil. Maybe more importantly, I have a 250K tubine test cell called a 5 cup swirl section test that is hooked up to a room full of measuring equipment. I can tell you CO2/CO/particulate/NOX/SOX/Unburnt fuel/temp (both axially and radially) and about 100 other combustion related parameters along the flame path every centimeter. I can't tell you what this is for because it is top secret. However, I will tell you what. You are wrong in nearly every statement above. My suggestion is to continue questioning people statements because that is good. However, I would also suggest to use some sort of data rather than your opinions.

Collin

 

[cwcross]

I have a problem with that equation, mainly with the logic pertaining to the linear scale of pH. How can you assume a linear scale when pH is measured on a logarithmic scale?

Cougra, you are absolutely right. I grossly oversimplified. Here is an article that applies the appropriate mathematics. It states something to the effect that doubling CO2 from 350 to 700 ppm will give rise to a 0.4 change in pH.

I was just trying to make a point. You are correct. Please enjoy the article and forgive my oversimplification. I was in a hurry between meetings.

http://www.advancedaquarist.com/issues/may2002/chem.htm

Best Regards...Collin

 

[cwcross]

Nice Article Nikki. I have added it to my collection. Thanks...C

 

[Cougra]

I have a freshwater planted aquarium where CO2 is deliberately pumped into the system. Obviously the pH falls slightly as a result (with a swing of less then 0.4), but if I cause any turbulence in the tank with powerheads, aeration ect all the CO2 is lost because it is extremely unstable in solution.

With the amount of turbulence we have in a saltwater tank the CO2 will disapate extremely quickly.

 

[cwcross]

I have a freshwater planted aquarium where CO2 is deliberately pumped into the system. Obviously the pH falls slightly as a result (with a swing of less then 0.4), but if I cause any turbulence in the tank with powerheads, aeration ect all the CO2 is lost because it is extremely unstable in solution.

With the amount of turbulence we have in a saltwater tank the CO2 will disapate extremely quickly.

Cougra, it is a little different in a saltwater tank because of the large amounts of carbonate and bicarbonate which depends upon the CO2 in the air via carbonic acid.

If you add too much of either carbonate or bi-carbonate into the tank, CO2 will either be drawn in or released to establish the appropriate equilibrium.

However, I'm sure you are correct. If you are oversaturating either fresh or salt water by pumping it in, then mechanical energy will affect this and cause the excess CO2 to be lost rapidly. A similar situation could be reached using a calcium reactor in a reef tank if too much CO2 is injected.

Sincerely...Collin

 

[NaH2O]

This is also incorrect.

Collin, are you indicating that the respiration of humans and animals in a home are not going to effect pH? The reason I ask is because Randy H-F indicated this in his article as one contributing factor.

 

[cwcross]

Collin, are you indicating that the respiration of humans and animals in a home are not going to effect pH? The reason I ask is because Randy H-F indicated this in his article as one contributing factor.

No, I'm sorry. I did not mean to give that impression. I'm not sure why you think I meant that, but I must have mis-spoke myself somehow. pH is definitely affected by ambient CO2 levels. It is strictly a thermodynamic fact. If respiration is such that CO2 levels rise substantially, then pH will be affected. CO2 in normal air is very low and in the ppm range. Thus even a doubling up to 700 ppm is entirely reasonable in my opinion. I have no direct data or experience with this myself, but I find it very reasonable. Furthermore, I have found no technical problems with RHF's articles yet. If he says this is likely to happen, I believe he has probably founded this statement on hard data.

A gas furnace will also raise CO2 if the flame is exhausted into the house. I am not an expert on furnace designs but I know that the old sort I had in my bathroom that is a gas burner and glows red would be one example.

I used to love that old heater. It got my bathroom nice and toasty on cold winter mornings.

Sincerely...Collin