redstrat

EDIT: opps didn't see hoppy's post please ignore this, I just repeated what he said basically.

Naja002

Makes sense. I just never really thought about it. The description that I read--probably a yr ago--basically said that it let's C02 Out and 02 in because of the pore size. But I guess what they were really getting at is: because the the pore size--it allows the gas exchange while keeping the Water in!


Sounds like a New Product for Seachem! Like their pH and Ammonia Alerts.....

Probably not much help, but: the Vacuum packers they sell at walmart, etc have a heat sealer for those types of plastic bags. If you know someone that has one........Maybe you could borrow it.

kamel_007

what do you mean with a shot glass??

it's just a small cup..

hoppycalif

Yes, and I completely missed that. I was obsessed with how to make a container that I could easily replace the membrane on at that time, not the membrane itself. It is still a great idea, and a really cheap source for membrane materials.

hoppycalif

The photo looked like the bottom of the cup was thick like a shot glass is made, so I just thought it would be a good joke! I keep being amazed at the variety of ways there are to make this little device. When I first thought seriously about it I assumed that the ADA type glass device was the only good idea - now we are down to a piece of tubing, a piece of breather bag and a rubber band!

dennis

I'm not so sure the breather bag idea works. I've had a couple differnt models in my tank for over an hour and there is no color change.

junco

Sorry if this has been brought up already, but I didn't have time to read the 15 pages of this thread

If I didn't want to take the time to construct one of these, or buy one... and just wanted to do a quick test to see if my KH/pH chart method is fairly accurate, could I do the following?

1) Take a piece of tubing and seal it at one end and bend it in a U shape.
2) Use syringe/pipette to put distilled water into one end of the U and secure underwater in tank somehow.
3) Let sit overnight, take out next day during peak light hours when respiration is moving right along.
4) Test the pH and KH of this water and compare to the chart to get current CO2 level.

Would this work? I don't really need a day by day view of this and just want to see if the pH/KH chart method is accurate enough for my needs. I wouldn't need to buy anything, construct anything, or spend an hour getting distilled water to be exactly 4 KH.

hoppycalif

If you are going to use pH reagent to find the pH of the water you need to adjust the KH of the water to around 4 or 5 dKH, assuming you will be measuring around 30-40ppm of CO2. The color is just too hard to judge accurately unless you are reading about 6.6 pH. And, plain distilled water won't work because it has no measurable KH, so it gives an ambiguous reading of CO2. But, the device you describe will work fine.

hoppycalif

Dennis, this idea has to work doesn't it? Assuming the breather bags really do allow CO2 and other gases to pass thru freely? The time it takes for them to reach equilibrium might be long, but I don't see how they can fail to work eventually. Tom Barr believes a device like this will have a short response time, but I haven't seen any data to say, one way or another. Of course a breather bag, used for its intended purpose, doesn't need to react very quickly. So, it is possible that the density of the pores in the bag material might be too small for the material to work rapidly for this.

dennis

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.