How to make a reference KH solution for CO2 measurement

[Plantbrain]

Given the wide ranges of KH related issues and suspiciously high CO2 ppm readings in some folk's tap water/tank water, this KH reference method is a very useful thing.

The hardest thing is getting folks to actually make one and calibrate things.

So I did some digging and have a couple of useful links that make it clear.
Here is a good KH Calculator using baking soda to make your KH reference sample.

http://www.cnykoi.com/calculators/calckh.asp

Note: make larger volumes(5 liters) and high concentrations, and then dilute.

This reduces errors(less is better).

So adding 5l of DI H2O (1.321 gallons) and 4.992 grams of baking soda = 40KH.

Play around with the calculator, try 50 liters and 4 KH, the higher volumes and higher the concentration, the less error you have, well up to a point[]

50 liters of DI water and 40 KH will give you 49.923 grams.
Now you have pretty high accuracy but you have a lot of KH solution!!
5 liters is not bad and you can toss the rest down the drain or trade to friends etc in the hobby.

Then you may take a 10ml sample of the 40KH reference and add it to a 90mls of DI water.

This will give you a reference of 4 KH to within a very close tolernace depending on how careful you are weighing the baking soda, measuring the water volume and cooking the baking soda for 30-45 min at 400F before weighing to remove water and CO2 in the baking soda.

For diutions:

http://www.wellesley.edu/Biology/Con...etovolume.html

This should help you get going on making the KH reference solutions and putting them to good use.

You may use the drop checker method, it's slow, cheap, simple, or you can DIY a DO membrane on the tip of a pH probe, and put the KH ref solution inside instead of the dissolved O2 KCL solution.

This is extremely accurate.
DO membrane material is fairly cheap per unit.

Regards,
Tom Barr

[dapellegrini]

Awesome... This is exactly what I was looking for to setup my Drop Checker when it arrives.

If you ever get an easy mod to fit on the end of my SMS122, I think I would do that too...

Thanks Tom

[Plantbrain]

Well, I'll see what they do, using a rubber hose that slips on the end of a pH probe and then another size larger over top of that to provide more surface area and then notching the outer hose to faciliate a grove for an O ring makes a simple water tight seal between the water and the KH solution and allows fast equilibration.

Very cheap once you have some poly membrane.
The KH solution is a snap to make.
I think a lot of folks will use the drop checker as it's easier etc, but there will be a crowd that likes the membranes.


Regards,
Tom Barr

[squawkbert]

I have GOT to make one of these...(well, 2 of 'em).

I think I'll try to just put some bends in a glass tube, mount w/ suction cups.

I have a microbalance & RO/DI at work & a moisture balance to cook the water out of some baking soda.

I'll get the indicator for xmas as part of a APA FW master kit... I think I'm set!

If I get good at it, I may buy dry indicator and premix test solutions of differing KH values and start my own ebay business. I'm thinking I can make these for <<$1 ea. (glass, propane will probably be the most costly parts).

[dapellegrini]

Nice! Make a simple end cap for my SMS122 prob and I would buy one of those from you too!

[Plantbrain]

BTW, a nice cheap scale can be bought on ebay for 10-20$ for measuring 4.99 grams of Baking soda, cook it first though.

Then if you can, find a cheap graduated cylinder etc on ebay also, or www.AquaticEco.com, chem supply place etc, they should be pretty cheap, or a volumetric flask etc to make dilutions and stock solutions for any range of of Nutrients such as NO3, K+, PO4, etc.

Then you can calibrate all those cheap test kits

Regards,
Tom Barr

[malkore]

I'm going to sticky this for a while to make sure everyone sees it. Thanks for sharing your wealth of knowledge Tom.

[dapellegrini]

Ok, so a few more questions now that I have my drop checker and am gearing up to make my kH solution.

- Cleaning the drop checker before use - I am assuming that a few rinses in the huge amount of kH solution that I will end up with would be sufficient?
- The water - Is "Distilled" water the same thing as "Deionized" water?
- The test regent - Is there a certain pH test regent that is best for this application? The regent that came with the kit was open in transit and had to be thrown away. I am considering using my AP pH test regent... Will this work?
- Refreshing the solution - How often, if ever. should I change the kH reference and Regent to maintain accuracy?

Once I have my kH solution baked up, mixed and measured, I plan on using it in the AP kit's pH test, then using that liquid, which will include the regent, to fill the drop checker. Does this sound right?

TIA

[squawkbert]

- Cleaning the drop checker before use - I am assuming that a few rinses in the huge amount of kH solution that I will end up with would be sufficient?

Yes

- The water - Is "Distilled" water the same thing as "Deionized" water?

Yes

- The test regent - Is there a certain pH test regent that is best for this application? The regent that came with the kit was open in transit and had to be thrown away. I am considering using my AP pH test regent... Will this work?

I think so (should be bromothymol, try it)

- Refreshing the solution - How often, if ever. should I change the kH reference and Regent to maintain accuracy?

when spilled, contaminated w/ tank water (got loaches?) or if it fades

- Once I have my kH solution baked up, mixed and measured, I plan on using it in the AP kit's pH test, then using that liquid, which will include the regent, to fill the drop checker. Does this sound right?

Just add the 4dKH solution you made to the drop checker, add a few drops of the pH reagent (hwo ever many it'll take to give decent color), that's it.

I'm loving the stickyness of this thread.

[dapellegrini]

squawkbert - Thanks!

One more: Concerning the air gap in the drop checker. Do I need to reduce the air gap or is it ok to leave as much as as possible in there? Will the amount of air between the aquarium water and the kH solution effect response times or accuracy?