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Hello,
I'm very new to all this. I'm not sure what you mean by distilled water for your drop checker and why that's important. Could you explain please? I'm assuming from your discussion that you can change the KH of this by adding bicarb of soda. KH is the water hardness right?! So it will be very different depending where you live in the counrty (I'm in the UK).

Sorry new to website and didn't realise there was more after 1st page!!!! Maybe there are answers in the other 19 pages!!!! Sorry if I have interupted your discussion on something else.....can I delete an entry and how?

Thanks
Claire :confused:
You use distilled water to make your 4dKH solution. If you use plain water, pH could be off as a result of something other than the bicarbonate.

PS - for you "real chemists" 4dKH corresponds to 0.06648mM Na Bicarbonate (if my math is right).
 

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Nice - I've been playing w/ some different membranes that are more commonly available (no luck yet).

Please post some part numbers or specs for the membranes you've got working!
 

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I wonder if some used clean-room type garment scraps would work, they're made of Tyvek but there's enough of a texture to them that sealing could be an issue...
 

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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.
 

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2 things

Regular drop checkers staying green - maybe (I'm speculating here) there isn't enough water movement around it, or it's too close to the outlet of the CO2... if CO2 actually displaces air in the checker instead of equilibrating with it, you won't get it back out unless you remove the drop checker so that regular air is mixed in again (CO2 is heavier than air and could blanket the surface of the checker, but I would think it would go yellow if this happened).

Also - it isn't faster (or slower) than the open types, but it won't leak, even if flipped... and it's super easy to assemble (2mL LC sample vial, some of Hoppy's probe membrane, 4dKH purified DI, API pH indicator solution):


The red thing is the setting knob from my Visitherm Stealth heater. It's a tight fit, but that's a christmas mini-light suction cup holding the checker to the inside wall of my 46 (also w/ new pic today - see sig. link)
 

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The membrane has replaced the PTFE/silicone rubber cap liner in the yellow cap (that has a big hole in it for instrument needles to pass through).

If your wife can bring you LC vials & some good water (high resistivity, polished, Milli-Q type) & you get some gas permeable membrane, you can make these things all day.
 

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That one is pretty easy to see. You should pull the ADA style one & yours above the water line, let both turn blue and see which turns green faster when returned to the tank.
 

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Nice job on the "3-jigger drop checker"
 

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Wow! What a neat and easy way to make one of these gadgets. The only suggestion I have is to keep the quantity of water in it to a minimum to speed up the reaction time.
Hoppy - I suspect it (speed) may also be a function of surface area than of volume in the "air gap" checkers. I've got one (air-gap one) that holds <2mL of indicator solution but it's in a tall, thin shell vial. It reacts slower than the membrane one (inverted bottle w/ hole in cap) in the same tank.

Once, it went yellow so I pulled it and stuck it to the outside of my tank, it took 3 days to change back to green. My membrane one went from blue to green in 3-4 hours when I added it to my 5g tank.

I need to refill the one in my 46g tank as the 96W light has not been kind to the indicator dye. I think I'll mount it a lot lower in the tank when I refill it (maybe in some shade provided by the sword that's taking over).
 

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http://img479.imageshack.us/img479/5952/20070122fts5g3pz.jpg

^pic featuring a poorly designed air-gap DC - it's super slow to respond to change because of the ~3mm diameter at the top of a ~3cm column of indicator solution. Something along the lines of the shot glass design featuring a short, wide column of indicator solution should respond a lot faster (I feel another science fair project idea coming on).
 

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My reading indicates that there's ~300ppm atmospheric CO2, ~3ppm of which is willing to dissolve into aquarium water. In streams, lakes etc, you get more than 3ppm CO2 in solution (underground, minerals, other organisms contribute to CO2 more in nature than in aquariums).

Note to MTechnik - I bet that checker didn't change color ove the course of Borat - the test tube appears to be too skinny. I'd suggest a fatter one and a lot less liquid in it (enough to get liquid column height=width should be good).
 

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OK - you've all covered this quite well and have made me ashamed at how much of this type of chem. I've forgotten.

The only little correction I can offer now is with respect to pH of carbonic acid solutions. Carbonic acid is a weak acid, so it will bottom out w/ respect to pH somewhere around 5.

Good discussion!
 

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Assuming your baking soda is anhydrous (don't bake it out, undesirable chemistry will occur) - best to use a new box, dig down a bit...

I think these are the corrected values...
60.06mg per liter of RO/DI water = 4dKH
74.60mg per liter of RO/DI water = 5dKH

Now let's assume you don't have a balance that can accurately weigh out mg.
So the alternative is to make a more concentrated solution, then dilute.

6.0g per 5L RO/DI water = 80dKH (we'll call this the stock)
(1.20g in 1L will also work, if your balance is accurate enough)

1 part stock diluted to 20 parts total volume = 80dKH/20=4dKH - even multiples will also work. For example, 10mL stock + 190mL RO/DI=200mL total at 4dKH

25 parts stock diluted to 400 total parts = 80dKH*25/400=5dKH that would be 25mL stock + 375 mL RO/DI.
 

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i got a scale for my guns and it goes to the .000 i think i put something like .029g in a gallon of distilled water. Correct me if this is wrong. It looks as if its working.
0.029g=29mg, 1g water = 3.786L

29mg/3.786L=7.659mg/L, assuming it's dry bicarbonate.
For 4dKH, you need 60.06mg/L of dry bicarb, more like 75mg/L if your bicarb is 19.5% water (like mine was).

If my math is correct, your chedker should be going totally yellow at the first hint of CO2 (green at 3ppm, what you would have w/o any CO2 addition) as you're in the 0.4-0.5dKH range.
 

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^ not really, though together, they will cover a larger range. The 3dKH one will cycle from blue to yellow and stay yellow as the 4dKH one starts to think about going green. I guess if 3d is yellow and 4d is blue, you're somewhere near 10-15ppm(?-been a while since I looked at the charts).
 
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