This is the thread to place the various adaptations of Vaughn's reference idea for the drop checker and the pH reference probe based upon the same principle.

The goal of using a KH reference solution is both simple and elegant.
Many folks have variations and issues determining their KH in terms of precise amount and one without interferences from other things such as tannins, peat, ADA aqua soil among other issues such as anythuing that influences non carbonate alkalinity and other acids than CO2 gases.

There are a few issues bu they are resolved and almost done with the pH probe.

The purpose here is to detail out each method and the various trade offs and advantages each has. They are essentaially the same as the pH colormetric cheapy test and that of the pH probe for measuring the pH against a a Kh test measurement.

The issue has not been so much the pH test, rather, the KH.

Vaughn asks from the APD:

"So, do you envision this as a product we would buy from the
probe
manufacturer - A CO2 probe?"

Sort of.


" The only downside I see to that is that
it offends my DIY sensibilities, but I do notice that I haven't
been
trying to make my own pH probe either, so I can hardly object."

It's no different than what we have today, the DIY cheaper
versions will and are colormetric, DIY drop checkers are every
bit as good as a colormetic cheapo test kit, with the KH
reference solution they are better.

So DIY and cheaper folks can take advantage of the method you
suggested using the KH reference solution.

The pH probe version is still a pH probe, just added a screw on
DO membrane and have a company just adapt it for our specific
use.

It might cost 25-40$ more than a cheapo pH probe many folks use
those also.

You can DIY pH probes, thermo couplers(temp probes) and Redox
probes etc as well, but most just buy those.

Same deal here, you can adapt a pH probe, but most will not.
It's nice to dIY, but it's also nice to have a company make it
for those that do not want to deal with DIY.

Basically it changes little in terms of the DIY/store bought
issue we have **right now**, without the KH reference solution
modification.

" I'm
guessing that this will be a nice lab instrument for the
"serious"
hobbyest, not the dilettante hobbyest like me. And, I don't
have
much doubt that it will work.

Vaughn H."

Naw....
All we do is add a screw on cap that works on DO probes to a pH
probe.

We add different solution inside, baking soda vs KCL.
This adaption should and dose work fine according to the
companies that make the Teflon and poly membranes(I spoke to
them as well as AM and Milwaukee).

Regards,
Tom Barr

www.BarrReport.com

Speaking of DIYing a pH probe: I have a Milwaukee portable pH meter that seems to still work ok, even after I neglected it for several months. The business end has a cap on it, where you are supposed to keep some water to keep that end wet at all times. I wonder if I could cut a hole in the end of the cap, cover the hole with semipermeable membrane, add the reference KH solution in the cap, reinstall the cap and use the assembly as a CO2 probe? See my crude sketch below:

What is the major downside to cutting a hole in the cap that way? I could continue to store the probe with water in the cap, but it would let atmospheric CO2 enter the water.

This post, this morning on APC, DIY Drop Checker - Page 13 - Aquatic Plant Central- aquascaping...a living art started me to thinking more about making a DIY CO2 probe. So, this afternoon I visited my local Home Depot, found their bin of Tyvek, helped myself to a 3" square of it (so, sue me, I swiped it!), and now I'm chomping at the bit looking for progress!

I've reported you to the Sacramento police dept

The rubber wet caps should work fine, the real issue is water leakage into the rubber cups at the membrane seal and also a rather obvious problem, the cost per unit of membrane.

The AM and Milwaukee's are cheap and easy to just screw on.
The plain membrane cost a lot more and you have to DIY it.

Cost is important here as well.

I want the item to marketed and sold, this will make it much more consistent and available and it should not much more than the cost of DO caps, about 8-10$

Milwaukee Replacement Membrane for SM600 Dissolved Oxygen Mete

And no KCL solution but a ref KH solution.

Same type of deal, just made to fit a pH tip is all.

A rubber DIY can be done, I have some new material coming in in a few days.

I think epoxy on a rigid holder would work well for gluing it on. I used an O ring that was very tight. Then slip it down a bit and used a hypo needle to add the KH solution, you ALSO can do the filling before adding the O ring.
This is a bit easier to do and less air bubbles inside.
OSH, Home depot sells all sorts of O rings FYI.

Still, 8$ ain't really saving you much for a DIY pH membrane ref probe adapter don't you think?

Heck, that would not even pay for my time to go buy it and come back.

Very simple upgrade and cheap, pre made for added consistency amongst it's users and availability., Folks can still DIY, mind you, but for saving $ on a DIY project when the item will not cost to start with?

I have some sheets of PTFE membrane coming but have not figured a per unit price for each DIY.
These are the most sensitive to changes in O2/CO2 properties.

Artifical lungs are often studied and they use such membranes to exchange the CO2 and O2. Our lungs are still about 5x as good as the best artifical membrane.

Regards,
Tom Barr

Are there any updates on the membrane material?

What has been tried an what works best?

Thanks,
Bill

We have been discussing using Kordon Breather bags as membranes on APC, and Dennis is trying the idea now. So far, without success. I expect to have a couple of the bags in a day or so, and I will experiment with them too.

They are way too slow.

Regards,
Tom Barr

That has been Dennis's experience so far, but he had a bubble of air above the KH water when he tried it, which would slow it down even more. The last he posted it was taking more than 3 hours for any color change to start up.

I could have told you that to start with

Use the poly membranes or the teflon.
They are the best and the teflon tend to tougher and last longer, but are not as sensitive to changes.

No need to suggest which I prefer

I use a 10mm O ring, add the KH solution inside the space, the pH probe is 12 mm, so this makes a nice fit.

I'm still not sure how long between ref solution replacements I need to do yet.
It's still pretty new, they do make a ISE type CO2 probe that is similar, this is just a simpler cheaper DIY probe, the pre made CO2 probe runs about 395$.

I prefer the 50$ ones and the 5 $ of materials.

I sold off my old pH meter and replaced it with a nice Hanna pH/Redox/Temp/ISE meter for home use.
So I have some interesting work ahead with respect to plant tanks.

Regards,
Tom Barr

Hi Tom,

I did a search and there are a lot of different poly membranes out there. Do you have any suggestions on a particular one and a source for them?

Thanks,
Bill

The type of material used as a membrane also critically affects the performance of the system. Some have found that 0.001" to 0.0009" thick polyethylene, which is readily available from normal sandwich bags, works best for O2.

Membranes that are more oxygen permeable, such as TFE Teflon or silicone, may be required for experiments at low temperatures or when a response rate faster than 4 seconds is desired. However, these materials will cause a greater motion artifact because the concentration gradient extends further into the bulk solution. TFE Teflon will also stretch and thin over time, causing the initial amplifier calibration to become incorrect. FEP Teflon usually works well, but is too stiff to wrap around the small electrode tip. Saran type wrap is not sufficiently permeable to oxygen to be useful as a membrane.

The structure of sandwich bags tends to be poor even if the base material is the same.


Regards,
Tom Barr