# "Degassing" a Water Sample



## hoppycalif (Apr 7, 2005)

I have for some time believed that our use of the CO2 measuring technique where we take a water sample from the aquarium, let it sit for 24 hours, measure the pH of that sample, then try to lower that pH by 1.0 in the aquarium, is very inaccurate. My previous experimenting indicated that the pH we measure for the degassed sample can vary considerably depending on how long we let the sample sit out in the air. On the Barr Report, several months ago, another experimenter found much the same thing.

So, I did another experiment this weekend. I mixed up some distilled water with a trace of bicarbonate of soda in it to get water with 0.35 dKH. I did this by mixing a little of my 4 dKH water with more distilled water. To measure such a low KH I used ten times the volume of water the test kit calls for, and counted each drop of reagent as .1 dKH (Aquarium Pharmaceuticals test kit).

I introduced CO2 by blowing into the water with a short air hose for about 30 seconds. Then I sat the sample glass on the kitchen counter and left it for about 50 hours, measuring the pH of a sample of that water every few hours. Below is a chart of the test results:









You can see from the chart that it took at least 30 hours for the pH to achieve an equilibrium with the atmosphere, and the equilibrium point was about 2.5 ppm of CO2, but the inaccuracies in measuring pH and KH make that number be about 1 to 4 ppm.

Now I am still uncertain about whether this is a valid method for checking CO2. The method relies upon the 1.0 pH drop meaning the in tank water has ten times the ppm of CO2 as the "degassed" sample. So, the range of 1 to 4 ppm for the degassed sample means the tank would have 10 to 40 ppm of CO2 if the pH were dropped by 1.0.

I am posting this only because I find it interesting, and because once again it illustrates just how hard it is to measure how much CO2 we use in our tanks. The ADA-style "drop checker" method still looks to be the most accurate method we have.

Soon I plan to verify that the ADA-style "drop checker" actually does have the same ppm of CO2 in the bulb as is in the tank water, and approximately how long it takes to reach that point. Stay tuned!!


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## MrSanders (Mar 5, 2006)

I agree with you 100% on this one.... In my tank if I take a sample of water and allow it to degas I end up with a PH of 7.4.... however I can easily run the PH in my tank down to 5.8 with little fish stress.... a drop in PH unit of 1.6

I think that it clearly proves that amount of CO2 in the degassed sample can and will vary GREATLY.... depending on many factors... 

Again another ballon busted.... that method of checking for CO2 concentration is just as useful as comparing the PH and KH in my tank water.... 

Doest tell me jack..... I to am messing around with the new drop checker method.... Using one of those little cheapo red sea ones.... it changes color well... However I am no where near convincenced that this method has any accurcy to it either.... time will tell I suppose


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## epicfish (Sep 11, 2006)

MrSanders said:


> I to am messing around with the new drop checker method.... Using one of those little cheapo red sea ones.... it changes color well... However I am no where near convincenced that this method has any accurcy to it either.... time will tell I suppose


Scientifically, it should prove to be quite adequate, given enough time for equilibration of the CO2 levels in the tank with that in the drop checker.

Oh, and given that the initial drop checker solution was prepared accurately, ie: 4 degrees of kH for a green color to indicate 30 ppm.


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## MrSanders (Mar 5, 2006)

> Scientifically, it should prove to be quite adequate


 should is always the key word though  haha, I hope that it does prove to be at least useful for us..... I personally am using distilled water with the KH brought up to 5...... right around a PH of 6-6.2 in my tank and the solution in the drop checker is green...... though I can still drop the PH all the way down to 5.8 or so.... however you can tell the fish have just "gotten used" to that higher end of CO2 concentration.... my discus hide when there is that much gas in the water, and all fish are breathing pretty hard.....

It will be intresting to see the gap between the amount of CO2 that is simply enough to have thriving plants and little algae..... and the amount of CO2 that fish can tolerate..... with all the problem solving going on by saying " your CO2 is low" I wonder if the concentration commonly recomended are really needed or if its just a sort of cure all that gets tossed around


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## epicfish (Sep 11, 2006)

Three limiting factors in plant growth that I see are:

1) Lighting,
2) CO2,
3) Fertilizers,

If you have good lighting with a decent photoperiod, that leaves fertilizers and CO2. Most of the time, it's CO2 that's lacking. Why? It's hard to measure the amount of CO2 in the water. Everyone goes with 2-3bpm. But what about their diffusion method? What about outgassing?

Personally, I think you should max out your dissolved and circulating CO2 as much as possible, up until the level at which fish stress out. Then you'll know for sure that your plants aren't starving for CO2.

The gap between the levels at which plants thrive and fish can tolerate depends exactly on your tank's conditions. ie: bioload (fertilizer), lighting, plants in the tank, water conditions, etc...that's why you should get the best lighting possible, pump up the CO2 to the maximum, fertilize on schedule, and hope for the best. =)

Another way to empirically determine the gap in _your_ tank is to do controlled experienments between the same plant, ie: riccia, under different growth conditions, ie: CO2 level and check for changes in the biomass of the plant...but hey, we're all in this hobby to look at the plants and fish and not to conduct scientific experiments on them...right? Well, some of us, at least.


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## epicfish (Sep 11, 2006)

MrSanders said:


> should is always the key word though  haha, I hope that it does prove to be at least useful for us..... I personally am *using distilled water with the KH brought up to 5...... right around a PH of 6-6.2* in my tank and the solution in the drop checker is green


That's why I said should. Are you sure your kH is 5? Is it 5.0, or is it 5.1? 5.2? 5.3? Is the test kit accurate? Have you calibrated with a known solution? 

That's why I said it *should* be accurate, depending on how accurate stock solutions are made and how they're calibrated. I wouldn't be suprised if test kits had kH/gH values up to -/+ 2 or 3 degrees of difference. Test kits expire too...is yours expired?  Unless you're uber careful, there's way too many factors to make 100% certain what you measure is infact that value. All we can hope for is a best-guess estimate of values.

You said the solution the drop checker is "green". What pH does it have to be for it to be green? What if it's 0.2 units off, is it still green?...etc. The responsiveness of the solution is also important.

This is a hobby...let it be a hobby! =)


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## MrSanders (Mar 5, 2006)

Dont you think your looking a little bit to far into it?


point being it would be nice to find a way to get close..... not know exact.... so its not a pure guessing game.... plain and simple.....


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## BryceM (Nov 6, 2005)

Interesting thread....

I have to admit, I had high hopes for the degassed method. The science behind it is much more solid than the KH/pH/CO2 chart. Still, it has shortcomings in actual practice as many have pointed out. Probably most of this is due to insufficient equilibration of the test water as Hoppy has pointed out. In my own tanks I still use it to get the CO2 into the ballpark, and then I adjust it slowly up while watching the fish. Once you know what the bubble count needs to be, keeping it there isn't too hard.

I suspect that just about any method of measuring CO2 will have some difficulty associated with it. The drop-checker idea is a good one. Time will tell how useful it is in actual practice. As it's essense, it's still just a pH indicator. The aparatus assumes that CO2 diffuses freely and rapidly into the indicator solution and that the indicator solution itself doesn't affect the results. It also assumes that nothing else diffuses into the indicator solution. This might not always be true in a system with lots of organic compounds floating around. Also, the concentration of carbonate in the indicator solution could change over time. If the osmotic load of the indicator solution is higher than that of the aquarium, water will tend to move from the tank to the indicator well to re-establish an equilibrium state.


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## hoppycalif (Apr 7, 2005)

guaiac_boy said:


> Interesting thread....
> 
> I have to admit, I had high hopes for the degassed method. The science behind it is much more solid than the KH/pH/CO2 chart. Still, it has shortcomings in actual practice as many have pointed out. Probably most of this is due to insufficient equilibration of the test water as Hoppy has pointed out. In my own tanks I still use it to get the CO2 into the ballpark, and then I adjust it slowly up while watching the fish. Once you know what the bubble count needs to be, keeping it there isn't too hard.
> 
> I suspect that just about any method of measuring CO2 will have some difficulty associated with it. The drop-checker idea is a good one. Time will tell how useful it is in actual practice. As it's essense, it's still just a pH indicator. The aparatus assumes that CO2 diffuses freely and rapidly into the indicator solution and that the indicator solution itself doesn't affect the results. It also assumes that nothing else diffuses into the indicator solution. This might not always be true in a system with lots of organic compounds floating around. Also, the concentration of carbonate in the indicator solution could change over time. If the osmotic load of the indicator solution is higher than that of the aquarium, water will tend to move from the tank to the indicator well to re-establish an equilibrium state.


There is no water connection between the solution in the bulb of the "drop checker" and the tank water, so no migration of carbonate ions can take place. Only things that exist as gases can do the migrating, including water, but only if there is a temperature difference between the two bodies of water.

What gaseous organics are in the water that affect alkalinity of water? I'm not a chemist, so I don't know, but no one has said there are any, as far as I know.

Yes, the drop checker is a pH indicator, and all dial type electric gages are miliamp meters, so...? What makes the drop checker work is the use of a known KH, in the range where green equals good, with water having no other source of alkalinity or acidity. The pH then is a direct measurement of CO2.

The test I am contemplating next is to fill a two cup measuring cup with distilled water with a KH of X (not sure what yet), put the drop checker in it with its water at a KH of Y (not sure yet), stick an air tube in the measuring cup and blow in enough CO2 to get the ppm up to around 15-20. Then watch to see how long it takes for the drop checker to indicate the same ppm of CO2 as a KH/pH check of a sample of that water indicates. The CO2 in the cup will be decreasing, while that in the drop checker will be increasing until they meet in the middle somewhere, then both will drop, possibly at the same rate, but not necessarily. Or, the theory that says both water bodies will have the same ppm of CO2 will be flawed. It should be interesting.


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## BryceM (Nov 6, 2005)

I might be wrong on this, but I believe that if you have two samples of water, one quite dilute and the other with a high ion concentration connected by an air bridge that water molecules will tend leave the dilute solution via evaporation and enter the concentrated solution via condensation.

Big effect? Maybe not, but it is a _potential_ source of error, especially over time. It will act to lower the KH of the indicator solution.

Carbonate can exist as a gas, or more correctly, it is in equilibrium with a gas. HCO3- is in equilibrium with CO2 when dissolved in water. When the CO2 in the aquarium rises, some of it diffuses across the air bridge to the indicator solution. It then dissolves. Some of it reacts with water to form carbonic acid, lowering the pH. Some of it reacts with water to form carbonate - it's own buffer.

The fact that CO2 is in equilibrium with its own buffer makes some of the CO2/pH chemistry a little difficult to work out.


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## MrSanders (Mar 5, 2006)

> I suspect that just about any method of measuring CO2 will have some difficulty associated with it. The drop-checker idea is a good one. Time will tell how useful it is in actual practice.


 I think that is how things are going to be.... for quite a while longer at least. There really is no sure fire way to know exactly how much CO2 there is dissloved in our tanks. I dont know what the optinum amount of CO2 is for our planted tanks.... however I do know that there is a certin point where plants thrive, algea doesnt and fish are comfortable...... I think the only sure fire way to get to that point is to use the "drop checker", or the "degassed methid" to get in the ball park..... thats its, nothing crazy about these things we arnt tryint to find out.... "ah yes! green does mean I have 29.627 ppm of CO2 in the water!"

We are just trying to achive a starting level which is close to where we want to be.... From there as it has already been said so many times to get to that "sweet spot" it must be a matter of expierence... watching your fish and plants while slowly working your bubble rate up...

For me using the degassed sample method, worked to get me closeyou could say.... however having a .6 PH unit to drop the PH down even further before fish really started to stress.... One could see how ever tank is going to be different and you really need to feel it out slowly.

My .6 unit of lee way, could be anothers .2 I guess thats where expierence and patience come into play to slowly add more CO2 until you get to where you need to be


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## hoppycalif (Apr 7, 2005)

I have read that our fish will acclimate to higher levels of CO2 over time, but I don't know if that is true, nor how much time is involved. If it is true, one could have a tank at X% CO2, with "happy" fish, but when adding a new fish, be unable to keep it alive. Does anyone have a feel for the acclimation effect as to about how much more CO2 an acclimated fish can tolerate, and how long it takes to reach that point? I know no one can say the acclimation effect is 11.7 ppm of CO2 and it takes 37 hours to get there, but is it something like an additional 20 ppm or 2 ppm and does it take hours or months? 

When we slowly edge our CO2 bubble rate up are we just acclimating the fish or are we coming closer to the nearly fixed limit on ppm of CO2 that the fish can tolerate?


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## BryceM (Nov 6, 2005)

I think you're on to something here. I know more about the physiology of humans than fish, but the comensatory biochemical processes that occur in humans take somewhere between hours to days, depending on which change you're looking at. I have frequently had issues adding new fish to a high CO2 tank. Some have looked very near death after only a couple of minutes. At it's worst, I've removed the fish back to their original water container, turned the gas off, run an airstone for an hour or two and had no further problems when re-introducing them. I've then resumed my regular bubble count after a couple of hours and the fish then seem to do just fine.

There is an upper limit past which no fish can compensate, but I suspect it's different for every species. Labyrinth fish might do ok at any CO2 level - who knows?

I think they do acclimate, somewhat. It does cost them metabolic energy to "work-around" the poison gas we're adding. The high CO2 levels may or may not have long-term consequences - certainly it doesn't help.

My gauge for fish health has always been spawning behavior. If they're spawning ok, they're probably doing just fine.


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## MrSanders (Mar 5, 2006)

> When we slowly edge our CO2 bubble rate up are we just acclimating the fish or are we coming closer to the nearly fixed limit on ppm of CO2 that the fish can tolerate?


 This is another very good point brought up.... and something to be careful with for those who do go about adding CO2 by slowly adding a little bit by bit until fish are noticable gasping at the surface. I have lost a few fish when adding them to my tank with no other explantion than this?

Another point that makes me wonder if adding that much CO2 is truly needed for plant health.... using the drop checker method and water inside of it with a KH of 5.... It is green when I hold my TANK water at a PH of 6.0-6.2
My fish dont start to clearly show stress until CO2 pushes the PH down to 5.8.... thats a pretty big gap in terms of CO2 concentration.... now on the other hand I have yet to see if play growth suffers from backing off the CO2 that bit.... however I dont feel it is going to, but time will tell on that....

I can tell you my fish look a whole lot more happy though....


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