Aquarium Advice - Aquarium Forum Community - View Single Post - How to make a reference KH solution for CO2 measurement

dapellegrini · 03-18-2007, 02:21 AM

The concept of a drop checker is very simple and elegant. You do a pH test with your favorite pH test kit (normal, not high, pH test range) using your aquarium water. Now, instead of throwing the test solution away, pour it in your drop checker and put your drop checker in your tank.

Whatever style drop checker you use, they all work on the same concept. You have your test solution separated by an air gap and on the other side of that air gap is your tank water.

Now... we all understand that if you can get your pH and kH, you can find a chart that will tell you how much CO2 you have in your tank. Well, the only difference between the test water in the drop checker and your aquarium water is the CO2 level (and the pH regent I guess, but we won't worry about that). As it happens, the CO2 passes through the air gap from your aquarium into the drop checker and over a period of time, say 1-2 hours, equalized with the liquid in the drop checker. So as your pH goes up or down (assuming you are inject CO2 somehow) the color of the liquid in the drop checker will confirm this change in pH.

So, now that you understand how a drop checker works you can start picking it apart. There are many other factors in your aquarium water that can change your pH and kH besides CO2 injection (think Aqua Soil, Phospate Dosing, etc)... Also the ideal color of the pH test solution really depends on what your tank kH is.

In step our use of a reference solution. Instead of putting tank water in your pH test, use a lab certified (or mix up your own) solution of distilled water and kH. Using a 4dKh reference solution for example, gives you an ambient 7.6pH with distilled water. In your pH test this will show up blue. Put it in your tank, which most likely has a different pH and kH, and let the CO2 equalize across the air gap into your reference solution and now you have a much better measure of CO2. Using the 4dKh reference example, once your pH in the Drop checker reaches 6.6pH, referring to the pH/kH chart, you have 30ppm of CO2. As it happens (not by any mistake) your pH test kit turns GREEN at 6.6pH. If you keep adding more CO2, the liquid will turn yellowish, if CO2 decreases in your tank, the drop checker will turn blueish...

Using a reference solution you remove all variables that could change pH/kH except CO2, making it a much more accurate way of measuring and monitoring your CO2.

I use mine with a fully automated system for a few reasons: (1) after you use a pH meter for a period of time you will start to see it become inaccurate and require frequent calibration. It is also only measuring pH and you are assuming that your kH is what it was last time you tested (not always a safe assumption. (2) your pH meter will not scream at you or otherwise let you know if your CO2 tank is out of gas, your solenoid is stuck open or shut, etc. On more than one occasion my Drop checker has been my first indication that my CO2 had run out.

I could go on, but this is already a lot longer than I had planned... I hope this helps a bit.

03-18-2007, 02:21 AM	#28
dapellegrini Aquarium Advice FINatic Join Date: Sep 2003 Location: Phoenix, AZ Posts: 870	The concept of a drop checker is very simple and elegant. You do a pH test with your favorite pH test kit (normal, not high, pH test range) using your aquarium water. Now, instead of throwing the test solution away, pour it in your drop checker and put your drop checker in your tank. Whatever style drop checker you use, they all work on the same concept. You have your test solution separated by an air gap and on the other side of that air gap is your tank water. Now... we all understand that if you can get your pH and kH, you can find a chart that will tell you how much CO2 you have in your tank. Well, the only difference between the test water in the drop checker and your aquarium water is the CO2 level (and the pH regent I guess, but we won't worry about that). As it happens, the CO2 passes through the air gap from your aquarium into the drop checker and over a period of time, say 1-2 hours, equalized with the liquid in the drop checker. So as your pH goes up or down (assuming you are inject CO2 somehow) the color of the liquid in the drop checker will confirm this change in pH. So, now that you understand how a drop checker works you can start picking it apart. There are many other factors in your aquarium water that can change your pH and kH besides CO2 injection (think Aqua Soil, Phospate Dosing, etc)... Also the ideal color of the pH test solution really depends on what your tank kH is. In step our use of a reference solution. Instead of putting tank water in your pH test, use a lab certified (or mix up your own) solution of distilled water and kH. Using a 4dKh reference solution for example, gives you an ambient 7.6pH with distilled water. In your pH test this will show up blue. Put it in your tank, which most likely has a different pH and kH, and let the CO2 equalize across the air gap into your reference solution and now you have a much better measure of CO2. Using the 4dKh reference example, once your pH in the Drop checker reaches 6.6pH, referring to the pH/kH chart, you have 30ppm of CO2. As it happens (not by any mistake) your pH test kit turns GREEN at 6.6pH. If you keep adding more CO2, the liquid will turn yellowish, if CO2 decreases in your tank, the drop checker will turn blueish... Using a reference solution you remove all variables that could change pH/kH except CO2, making it a much more accurate way of measuring and monitoring your CO2. I use mine with a fully automated system for a few reasons: (1) after you use a pH meter for a period of time you will start to see it become inaccurate and require frequent calibration. It is also only measuring pH and you are assuming that your kH is what it was last time you tested (not always a safe assumption. (2) your pH meter will not scream at you or otherwise let you know if your CO2 tank is out of gas, your solenoid is stuck open or shut, etc. On more than one occasion my Drop checker has been my first indication that my CO2 had run out. I could go on, but this is already a lot longer than I had planned... I hope this helps a bit. __________________ LIVE IN ARIZONA? COME CHECK US OUT!