Aquatic Plant Forum banner
161 - 180 of 358 Posts

·
Premium Member
Joined
·
7,436 Posts
Discussion Starter · #162 ·
I think Tom is getting that notion from the fact that he plans to use DO probe membranes. The DO probe has a fast response time and works basically exactly like he has described in his posts. As usual though, I don't follow his notion of cheap since I can't find any that are less than ~$25 per membrane. I obviously don't know where he is looking as he never tells....

The breather bags should work in theory though don't know exactly how they work. There might be an issue with pressure across the gradient, or lack of with water on both sides. I really don't know much about osmosis type functions, other than the basics of things wanting to be at equilibrium.

I'll let them float around longer. It is possible that there is to large an air space above the indicator sample. Let me say what I did... I took a small specimen jar with a snap on lid, about 10ml volume. I cut away most of the lid leaving only the outer rim. Placed a small piece of Kordon bag over the opening and snapped on the lid rim. Works great. The hole in the lid is about 1/2" diameter. I added 1ml to this and placed it inverted in the aquarium so that the indicator solution is sitting on the Kordon. I also made another that has a 3/16 hole but the container is 7ml and I used 2ml of solution. This one is tall and skinny compared to the first with is shorter and wider. Neither is showing a color change after ~3hrs.
With the air space sitting above the KH standard solution it will moderate the change in ppm of CO2 in the KH liquid. The air space has to reach equilibrium with the KH liquid as the KH liquid is reaching equilibrium with the tank water. So, wouldn't that just slow down a regular drop checker even more? By forcing the tank water CO2 to go thru the membrane holes instead of through a big air/water interface? I'm still betting that eventually the color will change as expected. And, intuitively I would say the smaller the quantity of KH water divided by the area of the membrane, the faster it could react. So the ideal would be a .030 thick layer of KH water with a membrane on both sides having a square inch of area. I haven't made any effort to prove this, nor do I know how to start to do so, but if I get bored I will make the attempt, at least to do it with a mind experiment.
 

·
Registered
Joined
·
2,988 Posts
Might sound Crazy, but before you give up---how about flipping the membrane around and trying it that way?

Maybe they only let 02 in and C02 out--who knows? :rolleyes:

If it works after flipping--I would say the it won't maintain equilibrium, but would be like a one time reading.......Hope that makes sense.....:D
I tried that when there was no change after about 2 hours;)
 

·
Premium Member
Joined
·
7,436 Posts
Discussion Starter · #165 ·
Dennis, do you have anything new to report on your testing with Kordon breathing bags? I just got a few from Bill Harada to play with, and the first things I notice are that the bags are covered with lots and lots of writing, part of that writing says it doesn't work under water. That surprises me, and I don't really believe it. If a gas can pass from the air to the water and from the water to the air, I can't see a physical reason it can't pass from water to water. I plan to try a simple experiment to verify that.

Meanwhile, over on Tom Barr's forum, Tom says the bags will have such a slow response time they will not work. That doesn't surprise me too much, since the original purpose for the bags doesn't require much of a response time. Fish just don't breathe a whole lot of O2 in and CO2 out - they are kinda small. But, for a DIY drop checker, a fast response time isn't all that important either. Response time is only important if you are using this for lab experiments of some kind and want to see the effect of a change fairly quickly. (In my opinion.)
 

·
Registered
Joined
·
2,988 Posts
It does work but takes about 24 hours to get to equilibrim. It also never gets to the same color as my regular open end drop checker. The small holed unit never changes color and the one with 1/2" opening gets blue-green while the other, regular style is green/yellow.

The response time is actually so slow that it won't even stabalize over the photoperiod. :(

I still can't find a source for the Teflon Tom talks about. Ican find them listed but no prices or avialibility for seperate ordering. I wonder if by the time one goes through the 5 disks normally included with a DO probe that the probe needs to ba replaced as well. I see proces for the probes ~120. I don't know exactly what the membranes are made from, other than Teflon of which there are lots of types and thicknesses. I have seen the membranes listed as 1mm and .1mm but I assume they must be .1mm. I searched for .1mm Teflon sheet/film but there were lots of options of types, porosity, etc.
 

·
Premium Member
Joined
·
7,436 Posts
Discussion Starter · #167 ·
Back to the drawing board I guess. I still plan to try one of the breathing bags to see what I can find out, and I have a small piece of Tyvek to try the same way, not that I expect it to work at all.

I have been doing a lot of google and wikipedia research on gas permeable membrane and I have learned that I know nothing whatever about the subject. That is a challenge!
 

·
Premium Member
Joined
·
7,436 Posts
Discussion Starter · #174 ·
Dupont is selling samples of this material for $500 to $1000! Now, I don't mind spending $10 now and then just to experiment with, but that's about tops for me.

I am continuing to read up on gas permeable membranes, and I notice that silicone rubber is a good material for CO2 permeability, but I don't see where one could obtain thin sheet silicone rubber. And, I saw a hint that latex rubber also is gas permeable - which (blush) leads me to wonder about using condoms, the extra thin kind. Does that sound promising to anyone?
 

·
Registered
Joined
·
2,988 Posts
Tom said the stuff is cheap. I don't think he would be messing with it as a realistic thing for the hobby if it were not. Obviously we are not looking into the same sources as he is. This Teflon stuff you finding now is pretty new but DO probes have been around for ages. We're just not looking in the right places.

Don't you just love how he always wants to help but will never really share the important stuff?
 

·
Premium Member
Joined
·
7,436 Posts
Discussion Starter · #177 ·
I found CO2 probes of this type already exist for blood gas analysis. They have a gas permeable membrane with a carbonate/distilled water solution between the membrane and the pH sensor, just as Tom is proposing. Looks like once again someone has figured it out before us, and probably patented the design.

The Cole-Parmer membranes are intriguing, and I may decide to buy a package of them just to play with. But, the season, the other jobs (making a Murphy bed, producing two newsletters, finding a new camera, etc.) are interfering right now. I'm still wondering if an ordinary condom acts as a gas permeable membrane.
 

·
Registered
Joined
·
225 Posts
I am continuing to read up on gas permeable membranes, and I notice that silicone rubber is a good material for CO2 permeability, but I don't see where one could obtain thin sheet silicone rubber.
What about some thin, clear, silicon rubber tubing?

Some other avenues to explore are Gore-Tex and SympaTex, both relatively common fabrics. I think eVent is another brand, but I'm not sure.
 

·
Premium Member
Joined
·
7,436 Posts
Discussion Starter · #180 · (Edited)
I haven't found a source of thin silicone rubber tubing. The stuff we sometimes use for CO2 tubing is too thick and too opaque - mine is blue also. The secret of all of this is to find consumer products that use what we are looking for, so the price is reasonable. I'm still thinking about the Cole-Parmet membranes, and I did sign up with their web site.

Edit: I bit the bullet and purchased a pack of the membranes. It's my Christmas present to myself!
 
161 - 180 of 358 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top