DIY Co2 Meter - The Planted Tank Forum
 
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post #1 of 5 (permalink) Old 10-18-2006, 04:06 AM Thread Starter
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DIY Co2 Meter

There were some really interesting conversations on the APD today.

[APD] Using a reference KH with a pH probe meter

The idea is to use the same type of design as an ADA Co2 drop checker. The ADA Co2 drop checker eliminates the KH in the KH/PH relationship by using a set KH (using R/O). All you would have to do is have the pH probe in the KH solution, and have an air gap for Co2 to exchange between the solution and the tank water (see figure). Since you no longer have to measure the KH, then a normal pH meter, with an algorithm that mimics chuck gads chart, could give a Co2 reading.

CO2 = 3 x [degrees KH] x 10^(7-pH).

Maybe my next project, try some of the things out from this thread, but give a reading in Co2 ppm. Could probably put these things in line and get a reading that doesn't get skewed by ph buffer, tannins, etc.

DIY CO2 Controller - The Real Thing - The Planted Tank Forum

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post #2 of 5 (permalink) Old 10-18-2006, 12:04 PM
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IUnknown, looks like a brilliant idea! We were all looking at the pieces, but you put the two critical ones together! Excellent.

So to be real clear, the advantage here is removing KH uncertainty out of the quest for knowing the CO2 ppm in our tanks, right? If so this is great.

I can see the need for one of those nice little sphincter valves here. But a fw questions:

1) Do we know that gaseous CO2 is as soluable into the chemicals used as reference solution?
2) If we assume that is is equally soluble into this chemical as it is in water, does this process (and the drop checker) work due to there being equality of co2 concentrations in the two fluids (tank and solution)? Of is it just the the solution's CO2 concentration moves in reference to the tank, just not to the same degree?
3) Do you know if that reference solution is harmful if it accidently spills into the tank?

Good thinking though!

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #3 of 5 (permalink) Old 10-18-2006, 03:03 PM Thread Starter
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I still need to read up more about it on the APD. I think someone mentioned that Erik had come up with the idea awhile ago.

Quote:
1) Do we know that gaseous CO2 is as soluable into the chemicals used as reference solution?
Our refrence solution could be anything. R/O water with baking soda for example (2.5 kh). How do those calibrated pH packets work? from what I understand the Co2 would diffuse out of the tank water into the air gap and be absorbed by the solution the pH meter would be sitting in. Maybe someone else can chime in on how equal the Co2 would be.

Quote:
3) Do you know if that reference solution is harmful if it accidently spills into the tank?[/
Since we could make the refrence solution whatever we want, it wouldn't have to be. Could we just use R/O water? Does the pH/KH relationship work with plain R/O water? I think there are problems with a kh of 0?
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post #4 of 5 (permalink) Old 10-18-2006, 11:37 PM
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Originally Posted by IUnknown View Post
Maybe someone else can chime in on how equal the Co2 would be.
I hope so. Because given your responses to the other two questions, I think this is probably real doable - depending on the solution selected.

But question #2 is still a stickler IMO.

Steve - 33g reef and a 180g planted in need of a re-scape.
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post #5 of 5 (permalink) Old 10-19-2006, 12:05 AM
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If you seal up the top of an aquarium the air above the water and the water will reach an equillibrium with CO2 concentration. Now, if you add another bit of water, also connected to the air above the aquarium, it will reach the same equillibrium with CO2 concentration. So, both bodies of water will eventually have the same ppm of CO2 in them. That is why the idea works.

If you don't put an indicator solution in the "drop checker", but just rely upon a pH probe, the water in that "drop checker" is just water with a known KH made up of bicarbonate ions. It may not differ in any significant respect from the tank water, so it can't be harmful if it spills into the tank. If you add indicator solution to the water in the "drop checker" you are adding a tiny bit of dye and an even tinier bit of sodium hydroxide. Those won't be good for the fish, but the quantity is very, very small.

Here is a sketch of how the pH probe method could be built rather easily: Here is where you can get the sealing nut for the probe:Handles, Thumb Screws Captive Panel Screws, Stand offs, Handles, Connector Hardware, Lyn-Tron, Inc. - Spacers, Thumb Screws, Captive Panel Screws, Standoffs, Handles, Connector Hardware - Bolt Products Inc., Fasteners, Cable Ties, Distributor Standard


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