Squawkbert

The gas permeable nature of the membrane is not such as to allow the rapid forceful pushing of air through it (maybe if you made an evening of it...).

Re paper idea... Oh well, it was worth a try. As soon as I get the membrane, I'll make the mini-autosampler vial version and get a pic up here.

I suspect it will work out pretty well and I already have the 4dKh/Indicator solution prepared...

I'm thinking that 4dKh isn't enough for my 46g tank. I'd been running just 1 1/2 gal. yeast reactor w/ a pretty good diffusion system and it's been showing green. I added another (full gallon) reactor 2 days ago... no color change. The checker in my 5g stays green/borders on yellow, but it has its own 1L reactor w/ a good airstone right below the filter 'waterfall' output.

hoppycalif

I understand what you are proposing. And, I think it would work, but it might take a few minutes to push the air out, plus you would have to be careful not to push hard enough to push the membrane off the end of the syringe. It would look clunky, but should work ok. If you try this, try to keep the amount of fluid small enough that the thickness of the fluid in the syringe is only a 1/16" or less. The thinner the layer of fluid, the faster it can respond. Another problem you would need to solve is how to see the fluid color. If you use tyvek you can't see thru it, so the only way you could see the color is thru the side of the syringe.

banderbe

I am using a drop checker from Hong Kong. I made 4 dKH water from RO/DI, put it in the drop checker along with six drops of AP pH test.

It was dark blue, and within a few hours was light green bordering on yellow. Great!

Well, the weird thing is that the drop checker water stays that color, even after a night of no CO2 and surface aeration with an air stone.

Seems pretty weird to me.. I would expect it to return to a blue color..

schaadrak

As soon as I posted that I thought to myself, "How the Heck are you supposed to see the solution through the plunger?"

Oh well, I did come up with another suggestion. You could assemble it while submerged in the solution. Meaning put the container in a larger container that is filled with the indicator and then attach the membrane.

And also I came across these while in my garage:


There little containers of paint that you can get just about anywhere. They're small, transparent, water tight (maybe) and cheap. What I figure I'd do is cut off the bottom and glue a piece of an Tyvek envelope to it. Then fill the container with indicator solution and snap the lid on and *BLAMMO!* instant DIY drop checker. When the indicator solution goes south, flip open the lid and change solutions. Simple, eh?

The only problem I can think of is water and/or solution wicking between the lid and the top of the container. If the container is full of water and I squeeze it hard enough (probably harder than any pressures it will actually endure while in the tank) a small amount of water seeps out at the hinge. I'm not sure if the gap is there because of warping and flexing of the sides from me squeezing it or not so I'm currently performing an experiment. I've filled the container with water and red food coloring and put it in a bowl of plain water. Over the course of the next few days, I'll check to see if the food coloring has leeched into the plain water.

Here is the container floating in the "Test Chamber":


It's cap side down so that the entire cap-to-container junction is completely submerged. If it passes, the next test is to put some indicator solution in the container and submerge it in a water and vinegar solution and observe if there are any changes over the course of a week.

I'll try to post every evening over the next week as to the progress.

Tschuss,

Kent

hoppycalif

That does seem weird. I am finding that the CO2 level in the tank drops very slowly, but by morning my drop checkers all show blue or near blue. And, I don't use an air stone at night, or increase the surface agitation. How are you turning off the CO2 at night? Obviously, I am thinking that you aren't really shutting it off.

hoppycalif

Now that is a simple, embarassingly obvious, solution to my problems with trying to get a very small amount of solution in my membrane drop checkers. I fell into the trap of mixing only as much solution as I needed, rather than waste precious water. But, there is no good reason for not mixing a cupful at a time, and dumping what isn't needed - other than the waste of indicator reagent.

Are those paint containers art paints, from an art supply store? They are most likely polyethylene, which is virtually impossible to cement anything to. But, a hole in the cap, with a membrane liner, with the cap doing the sealing and retaining of the membrane might work well. Don't forget, to get fast response you need to minimize the thickness of the "disk" of solution. The time it takes to reach equilibrium is proportional to the volume of solution and inversely proportional to the area of membrane. So, maybe cutting off the bottom of one of those containers, keeping just the lid and a thin section of the body, with the membrane covering the missing bottom, retained by the lid?

banderbe

A timer turns off a solenoid.. and I use a Red Sea 500 reactor so it's pretty obvious when CO2 is being injected because a bubble will form. There's that and the fact that the bubble counter attached to the canister doesn't show any bubbles

I guess it doesn't matter.. it just makes me a little suspicious of what the green color is really telling me..

I think I am going to try using the drop checker in a glass of tank water at equilibrium with the room.

I expect it should stay blue..

hoppycalif

Schaadrak's idea for how to load one of these things inspired me to try a new, even simpler design, but one which relies on an O-ring to seal the membrane where it is smooth, instead of trying to seal it by pressing the folds of the membrane to the plastic body of the device using a rubber band. This is what I came up with:


Once all of the acrylic cement, and the white nail polish dries well I will try loadiing it with Schaadrak's method, and sticking it in the aquarium.

But, I will have to make some more 5 dKH distilled water first - put on my Chemist's lab coat, with the pocket protector, etc.

banderbe

You know, I am wondering about something here.. the idea as I understand it is that the liquid inside the drop checker contains no acids and then after it is put in the tank, exchanges CO2 in the air pocket with the water from the tank until they are at equilibrium.

Fine, that makes sense.. but why won't other acids in addition to carbonic acid also enter the water in the drop checker?

I think the point of the drop checker was to isolate carbonic acid from other possible 'contaminating' acids in the tank water that render the usual KH/PH/Co2 calculation erroneous.

It seems like if there was say, tannic acid from driftwood that it too would enter the water in the drop checker..

I'm sure this has been covered.. so help me understand why we are so positive that CO2 is the only thing that can enter the water in the drop checker.

hoppycalif

The membrane is supposed to be gas permeable, but not liquid permeable. So, liquids can't pass thru it. And, as long as any gas on both sides is in equilibrium across the membrane, no net exchange of gases will occur either. So, if there is tannic acid on one side, but not the other side, the acid will be a liquid, which cannot pass thru the membrane. But dissolved gases are not liquid, so they do pass thru. I'm not yet clear on whether O2 and N in solution in the tank will pass thru the membrane but they should.

I found that if you just leave the membrane drop checker out in the air water vapor will pass thru it from the water inside to the low humidity outside, until the water is all gone. But, the indicator solution and the sodium bicarbonate seem to remain in the drop checker, leaving a very blue liquid there.

If you were to put a hot drop checker in cold water there would be water vapor passing from the drop checker to the tank, until the temperatures equalized. That would be from the higher vapor pressure inside the device than the tank water.