VahughH,
Just wanted to say that I love this method of yours - Great work !

As for mixing the solution: I started with 100ml of distilled water and a Nutrafin KH test kit. When adding the bicarb of soda I used the tiny measuring spoon that comes with a Tetra NO3 test kit, I don't know how much it holds, but it's tiny !

Initially I used the normal amount of water for the Nutrafin testkig (5ml) and added tiny amounts of bicarb, once was getting a reading of 4dKH, I increased to 10ml and repeated. As this was my first attempt at this method I stopped there.

Next time I'll go 4x the amount of water to achieve greater accuracy.

Al

Thank you Al! I wish I could take all of the credit for the method, but Dennerle was using it before I ever heard of it, and I really got the idea from "Gomer" (Tony Gomez), who casually mentioned using distilled water in the bulb instead of tank water, which led me to try to prove he was wrong about that. Like many of my "proofs" I ended up proving that he was right, and then just reasoned out why he was right. I hope the idea gets spread widely enough that all of the "aquatic plant gardeners" know about it. That's why I have become a nag in always recommending it on all of the forums I visit.

Well then I owe some thanks to Dennerle and Gomer ... but thanks for highlighting it

Well I've posted my attempt at this method on Tropical Fish Fourm's ( HERE ) just trying to spread the word a bit.

I'll certainly be using this method for now as it seems far more accurate than others.

Al

Al, I notice some are asking "how do you know that the ppm of CO2 in the bulb is the same as in the water?" The answer is: If there is a sealed quantity of air in contact with water which has CO2 in it, remembering that CO2 goes into and out of solution with water very easily, the air will soon reach an equilibrium with the water, with as much CO2 entering the air as is leaving it. Now, if that air is in contact with a sealed bit of water, that water and the air will also reach an equilibrium, with as much CO2 entering the water as is leaving it. No matter what the actual amount of CO2 in the air gap is, the equilibrium will be such that both batches of water will reach the same concentration of CO2. I tested this and reported the test on APC, at:DIY Drop Checker - Page 5 - Aquatic Plant Central- aquascaping...a living art. You might want to add this explanation to your discussion.
Edit: You can do a mind experiment to prove this too: Assume a large body of water "A", with CO2 concentration C1, connected to an air passage "B", with CO2 concentration C2 in equilibrium with C1, connected to another small body of water "D", with CO2 concentration C3. Now assume that C3 is less than C1, therefore not in equilibrium with C2. That means more CO2 molecules will move from B to D than from D to B, which raises C3 until C3 is in equilibrium with C2. But, at equilibrium, the concentration in air is C2, so the concentration that is at equilibrium with C2 must be C1, since we already said that concentration was in equilibrium with C2. So, C1 and C3 must be the same. You can use the same logic for the case where you assume C3 is greater than C1.

Many thanks VaughnH, I've posted that explaination.
Hopefully it will help to spread the word a bit further.

Actually now I've given this method a try and just re-read the APC thread it all makes much more sense than when I read it before actually giving it a go !

Cheers

Shane,

here is what has worked for me in creating my own ref KH solution:

0,6g of NaHCO3 into 100ml of distilled water make 200°dKH. If you enter 10ml of this solution into 490ml of distilled water you'll end up with about 4°dKH.

If you don't have a balance pharmacies will likely help you out weighing small amounts of NaHCO3.



Best regards,
Detlef

Thanks Detlev,

How accurate are the KH test kits like AP, etc? Can one use these test kits and get the results needed?

Well,

KH test kits don't seem to be very accurate which is not surprising though. See Tom's thread on "KH reference dosing". My cheapo Tetra test kit measured a little more than the calculated 4°dKH. It gave me around 5°dKH.


Regards,
Detlef

Ya, I have a test kit that uses titration to measure KH.

The Aquarium Pharmaceuticals KH test gives one dKH per drop of reagent in the test tube sample. If you use a double size water sample, each drop gives .5 dKH. And, if you use a 10X size water sample, each drop gives .1 dKH. The drops are not always exactly the same size, so the error in the test is probably around +/-10%, if not more. But, that isn't very important for measuring ppm of CO2, because the CO2 ppm is directly proportional to the KH, where it is proportional to ten raised to the power of 7 minus the pH. This makes pH errors much more significant. Fortunately the pH test is not at all sensitive to how many drops of reagent is used per test, so you can use the amount that makes the color most obvious to you.