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My 75 gallon

My 10 gallon.

Okay, so, I just put these into the tank (no co2 running yet, but I figured I might as well get these things in there now, just because). What I did was I added some amount of 4dk solution and about 4 drops of pH indicator from a test kit I had lying around. I used the pH indicator meant for 6-7.6, or something like that, not the high pH indicator that is for things above 8.

The test kit is at least a year or two old, so idk if that's a problem or whatnot. Did I set these up correctly? I know they are supposed to be blue but these seem really really REALLY dark. Should I get a newer pH indicator? Thanks for the help.
 

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The more drops of pH indicator, the darker it will be. Most people prefer 2-3 drops. 4 drops makes it too dark to easily read IMO. For example, we know the color in the photo should be perfect blue, because you told us you have no CO2. But it could as easily be a very dark green-blue, looking at the photo alone.

You used the right pH indicator, and they last virtually forever.
 

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Indicators have an equillibrium amount to visibly change colors. Too much indicator means it won't exhibit changes very well.
 

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Discussion Starter · #4 ·
So I should cut it down to 2 drops then? The amount of 4dk is also somewhat to taste right? At least enough to fill half way?

And does it matter how old the indicator solution is? I'll empty these out and re-do them, since I have enough 4dk and pH indicator to mess around with them.
 

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Indicator will go bad eventually. They normally have an expiration date. IMO I'd just go with standard API directions and do 3 drops to 5ml of 4dkh and use their color scale.
 

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Indicator drops are acidic. Note the color coming out of the bottle - they're showing their own pH. Plus they have their own, different kH. Adding too much indicator will change the overall pH/kH of the drop checker contents, skewing results a bit.

Amount of 4DKH also affects response time slightly.

But neither of these are significant enough that you should worry about them, unless you're tweaking drop checker performance for experimental purposes. Just use indicator and 4DKH "to taste".

Have not heard about the equilibrium effect Jeffww mentioned. Is this the same effect I described in different words, or something else? Would like to hear more about it.

In my experience, pH indicator lasts much longer than its expiration date. But you really should "test the test" to verify that. Safer to replace if expired, as Jeffww suggested.
 

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Indicator drops are acidic. Note the color coming out of the bottle - they're showing their own pH.
All the bromothymol blue solutions that I have prepared in the lab require a sodium hydroxide workup, so I do not see how they could be acidic in nature. Are you perhaps talking about how they behave as a weak acid in solution?

Plus they have their own, different kH. Adding too much indicator will change the overall pH/kH of the drop checker contents, skewing results a bit.
How does an indicator dye have a kH? I do not see any carbonate molecules contributing to it, aside from the small of CO2 that would dissolve into the dye.

Indicators have an equillibrium amount to visibly change colors. Too much indicator means it won't exhibit changes very well.
Have not heard about the equilibrium effect Jeffww mentioned. Is this the same effect I described in different words, or something else? Would like to hear more about it.
Not sure why adding more indicator would affect anything as well. Protonation/deprotonation is dependent on pH, and not on the amount of indicator dye present, last I checked.
 

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All the bromothymol blue solutions that I have prepared in the lab require a sodium hydroxide workup, so I do not see how they could be acidic in nature. Are you perhaps talking about how they behave as a weak acid in solution?
I say this because the solution comes out of the bottle yellow, suggesting it's acidic. Are your solutions blue or yellow by themself? If there's something trickier causing this, I'd love to hear about it.

How does an indicator dye have a kH? I do not see any carbonate molecules contributing to it, aside from the small of CO2 that would dissolve into the dye.
A kH of zero is still a kH! And it will dilute the kH of anything it's added to. If there's 3 drops of indicator, and 20 drops of 4DKH, then the final kH of the solution is actually 3.5. Which means we're all reading a bit higher CO2 than we really have...

I think it was Mistergreen who was experimenting a few years ago with making drop checkers work at lower CO2 ranges, by using a weaker kH solution. With such small levels of CO2 and kH involved, accurate kH is absolutely critical. He was getting unexpectedly high results. I ran this by him, he tried using fewer drops, and found it definitely made a difference.

Also, I've done some research into the origin of the claim that water at equilibrium with air has 3ppm CO2. It seems to be the result of someone else's low-range drop checker experiment, who did not account for the effect of the pH indicator on the overall kH of the solution. It's a false claim, totally unique to our hobby, believed only because it was repeated enough. All other scientific knowledge outside this hobby says it's under 1ppm (I forget the exact amount).

Fun stuff. ;)
 

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I started using the pre mix indicator solution that came from Green Leaf then switched to the solution where you add drops to RO water. I am using 4 drops added to an indicator bulb just over half full of water. The time it takes to change from blue to blue green is about the same so I assume that I have the correct mix. I have been turning my CO2 off before the indicator shows green as I don't want to hurt my fish. I assume that when the color begins to change from blue to green, (color is blue green), I have sufficient CO2.
 

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I say this because the solution comes out of the bottle yellow, suggesting it's acidic. Are your solutions blue or yellow by themself? If there's something trickier causing this, I'd love to hear about it.
The API pH test kit comes out yellow, I believe.

My lab prepared bromothymol blue is blue.

They both work the same (two drop checkers tested simultaneously).

A kH of zero is still a kH! And it will dilute the kH of anything it's added to. If there's 3 drops of indicator, and 20 drops of 4DKH, then the final kH of the solution is actually 3.5. Which means we're all reading a bit higher CO2 than we really have...
Are you suggesting that bromothymol blue solutions should be prepared in a bicarbonate solution and then worked up with sodium hydroxide?

I think it was Mistergreen who was experimenting a few years ago with making drop checkers work at lower CO2 ranges, by using a weaker kH solution. With such small levels of CO2 and kH involved, accurate kH is absolutely critical. He was getting unexpectedly high results. I ran this by him, he tried using fewer drops, and found it definitely made a difference.
Interesting, definitely, a lower kH solution could work to detect lower CO2 levels (the opposite holds true for higher kH solutions).

I am wondering though, when the solutions are prepared, what method are they prepared in? Unless you are using extremely pure reagents, weighing them out accurately, and then preparing them using volumetric glassware, there will probably be a large degree of error.

All other scientific knowledge outside this hobby says it's under 1ppm (I forget the exact amount).
I would love to see this data; or, perhaps someone here has access to a CO2 meter? :D
 

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They both work the same (two drop checkers tested simultaneously).
I suppose with zero (or near zero) KH, the acidity/alkalinity required to change the pH, and the color of the indicator, might be insignificant when introduced to a 4DKH solution.

Are you suggesting that bromothymol blue solutions should be prepared in a bicarbonate solution and then worked up with sodium hydroxide?
No, you suggested it. Not a bad idea either. Though I doubt many would bother, unless someone were to sell this premade. Want to make a few bucks? ;)

I am wondering though, when the solutions are prepared, what method are they prepared in? Unless you are using extremely pure reagents, weighing them out accurately, and then preparing them using volumetric glassware, there will probably be a large degree of error.
I couldn't say how they were prepared by other people.

I start with a reputable 4DKH solution, mix down with an appropriate amount of distilled water, and always prepare more than needed to minimize volumetric errors. Making 2DKH is super easy, just measure each part equally and individually; which eliminates any possible issue with inaccurate glassware.

Sure there will be some error, but still far less than any of the other errors we've been discussing.

I would love to see this data; or, perhaps someone here has access to a CO2 meter? :D
I've been asked that many times before, and I pretty much gave up bothering to give supporting evidence, since it's always ignored. But I like you and have enjoyed this thread, so I'll do it once more.

I Googled up a completely random source, one I'm pretty sure I haven't used before:

http://ion.chem.usu.edu/~sbialkow/Classes/3650/Carbonate/Carbonic%20Acid.html

The relevant bits - according to Henry's Law, at one ATM of pressure and 0.0355% average atmospheric CO2, the amount of CO2 in water in equilibrium with air is 1.2*10-5 mole/L.

Well I would have preferred ppm, but I'm sticking to the random source, so I have to convert. Multiply by the atomic weight of CO2 (C=12, O=16, 12+16*2=42) then by 1,000:

0.000012*42*1000 = 0.504ppm

Now if one example isn't sufficient for you, I invite you to look up your own additional references. But exclude those from the aquarium community. Doing so, you will find they all agree without exception, differing only by a slight amount based on what they assume to be average atmospheric CO2 levels. To believe different rules of physics somehow apply to aquariums? Denial at best, and there's a lot of it around. Even if some hobbyist finds 3ppm with a CO2 meter, I will question their meter, test procedures, or even honesty looooong before I believe aquariums are alternate universes contained in glass!
 

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No, you suggested it. Not a bad idea either. Though I doubt many would bother, unless someone were to sell this premade. Want to make a few bucks? ;)
Shipping costs would be more than the cost of the solution itself, and I doubt many people would be willing to pay ;)

I might toy around with it though.

I start with a reputable 4DKH solution, mix down with an appropriate amount of distilled water, and always prepare more than needed to minimize volumetric errors. Making 2DKH is super easy, just measure each part equally and individually; which eliminates any possible issue with inaccurate glassware.
:( If you're not making the initial 4 dkH reference solution, then there could be lots of errors.

I've been asked that many times before, and I pretty much gave up bothering to give supporting evidence, since it's always ignored. But I like you and have enjoyed this thread, so I'll do it once more.

I Googled up a completely random source, one I'm pretty sure I haven't used before:

http://ion.chem.usu.edu/~sbialkow/Classes/3650/Carbonate/Carbonic%20Acid.html

The relevant bits - according to Henry's Law, at one ATM of pressure and 0.0355% average atmospheric CO2, the amount of CO2 in water in equilibrium with air is 1.2*10-5 mole/L.

Well I would have preferred ppm, but I'm sticking to the random source, so I have to convert. Multiply by the atomic weight of CO2 (C=12, O=16, 12+16*2=42) then by 1,000:

0.000012*42*1000 = 0.504ppm

Now if one example isn't sufficient for you, I invite you to look up your own additional references. But exclude those from the aquarium community. Doing so, you will find they all agree without exception, differing only by a slight amount based on what they assume to be average atmospheric CO2 levels. To believe different rules of physics somehow apply to aquariums? Denial at best, and there's a lot of it around. Even if some hobbyist finds 3ppm with a CO2 meter, I will question their meter, test procedures, or even honesty looooong before I believe aquariums are alternate universes contained in glass!
Are you sure your calculations are correct? I haven't gone over all of (my) calculations yet, but I am getting ~3 ppm.

I am using the following references:

Hangx, S.J.T. Behaviour of the CO2-H2O system and preliminary mineralisation model and experiments. 2005.

Carroll J.J, J.D. Slupsky and A.E. Mather. The Solubility of Carbon Dioxide in Water at Low Pressure. J. Phys. Chem. Vol. 20, No. 6. 1991.

Lower, S.K. Carbonate Equilibria in Natural Waters. 1996.
 

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It was my understanding that if you added too much indicator, there would not be enough free electrons to change the color of the dye thus the color would not achieve the 10-100x change ratio to make visible color changes. In a lab where youre doing titrations with comparatively lots of fluid it wont matter but here when adding like 5-10 drops is like 20% of your total volume it matters doesnt it?

Additionally they do have their own ph and do make a contribution with enough dye. This also doesnt matter in a titration with a lot of liquid. Dyes also are slight buffering systems so theres that too
 

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Shipping costs would be more than the cost of the solution itself, and I doubt many people would be willing to pay ;)

I might toy around with it though.
Let me know if you do, I'll buy one.

:( If you're not making the initial 4 dkH reference solution, then there could be lots of errors.
I get 4DKH that's lab tested. May not be four nines accuracy, but come on. :)

Are you sure your calculations are correct? I haven't gone over all of (my) calculations yet, but I am getting ~3 ppm.
"Carbonate Equilibria in Natural Waters" on page 4 says:

"Water exposed to the atmosphere with PCO2 = 10-3.5 atm will take up carbon dioxide until, from Eq 2, H2CO3 = 10-5 M".

Edited slightly because everything isn't clearly representable here, with all the special characters; but enough to find the original text I'm referring to. I will note that by virtue of one of those special characters, H2CO3 in this context represents not just carbonic acid, but:

"the equilibrium mixture...mostly of the hydrated oxide CO2(aq) together with a small amount of carbonic acid"

Which is a fair enough representation of the available carbon from dissolved CO2.

10-5 (0.00001) is close to the 1.2*10-5 (0.000012) I previously quoted in my example. Again, we convert to ppm:

0.00001 * 42 * 1000 = 0.42ppm

It would be helpful at this point to see how you instead derived 3ppm from this.
 
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