[ofridagan]

Hello,

Some of you might remember my last project - AquaSketcher (original post)
Well, I just wanted to let you know that the AquaSketcher now has a new home on TheAquaTools.com
TheAquaTools.com is my new project. It is actually a collection of tools for the aquarium-keeper, the AquaSketcher is one of them (and apparently the most popular one).

Let me know what you think. Comments and suggestions are welcome!

 

[LetDiceFly]

I like your site, very nice. I liked the CO2 calculator by the shake method, except after some experimentation I found that there is a flaw in the formula (I think, I'm new so I may be wrong).

Using the numbers from my tank
KH is 5 dH
pH is 6.8 before shaking
pH is 7.9 after shaking
calculator tells me my CO2 is 6 ppm by the shake method

now if I put the numbers in the KH/pH calculator
5 kh & 6.8 I get 24 ppm
5 kh & 7.9 I get 2 ppm

Since the after shaken result of 2 ppm makes sense considering equalization with the atmosphere I would imagine that the 24 ppm is reasonably correct too. So there must be something wrong with the calculation that gave me 6 ppm.

 

[LetDiceFly]

I did a little algebra and came up with this equation. I assumed that the CO2 level after shaking is equal to 2. The 2 can always be changed to whatever is determined to be the equilibrium level of CO2. This result checks with the numbers I had in my previous post.

Let a = pH before shaking
Let b = pH after shaking

CO2 = 2 x 10^7-b / 10^7-a

 

[ofridagan]

I think you are right. Fixed it. Thanks!

The formula is now:
CO2 = 2 x 10^(b-a)

 

[hoppycalif]

Should be: CO2 = 2 times 10 to the a-b power. If the pH drop due to adding CO2 is 1.0 you have ten times the amount of CO2 that you had before adding the CO2. The only problem is that the amount you had before adding the CO2 is unknown.

Shaking a sample, or letting it sit in the open for a couple of days, or however you want to try to reduce the amount of CO2 to what it is in equilibrium with the atmosphere, doesn't give you the same result every time you try it. It can give from about 0.4 to about 4 ppm of CO2. Obviously ten times that is 4 to 40, not an accurate measure of CO2.

You can do some experimenting with this: start with distilled or deionized water. Add a tiny amount of baking soda to it to get a KH you can measure. Then stick a piece of airline tubing in it and blow bubbles for ten seconds or so. Now, start monitoring the pH of that water, measuring it every couple of hours or so. When I have tried this, the pH continues to rise for more than two days. Try it by shaking the solution, without sloshing it out. A problem is that the water starts evaporating as soon as you set it out in the open. That increases the KH. So, you have to monitor KH too.

 

[ofridagan]

Thank you hoppycalif!
I'm aware to the fact that this method of measuring CO2 is not accurate, it is meant mostly for someone who doesn't know his KH level.

 

[hoppycalif]

Thank you hoppycalif!
I'm aware to the fact that this method of measuring CO2 is not accurate, it is meant mostly for someone who doesn't know his KH level.

It isn't that it is inaccurate, it just doesn't give a usable result. If the probable error range gives you a value of 4 to 40 for the ppm of CO2 you haven't learned anything by making this measurement. At least the drop checker method gets you to a range of around 20 to 40, and is a very cheap method to use.

I apologize for raining on this idea, but I think it is important enough to know about how much CO2 you have in the water to make the effort to measure it with a usable method. I have expressed my opinion now, so I will stop belaboring the point.

 

[ofridagan]

No, no don't stop... help me make it better.
What is the "drop checker method" you mentioned?

 

[hoppycalif]

http://www.aquaticplantcentral.com/...aquarium-projects/32100-diy-drop-checker.html gives an explanation, even though it is a very long thread.