Drop Checkers/CO2 Indicators-Why and How

jonny_ftm

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Mar 5, 2009
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Hi all,

As I'm begining EI since 2 weeks (with a too great success I must say, as I have to prune my plants too often), I'm getting more and more concerned with CO2.

I have a PH meter controller, that I regulated based on my drop checker. I use a Dennerle drop checker with their stock solution (same colors as what I read here).

- Do you think it is ok to use such a commercial drop checker?
- How often should I change the solution in the drop checker?

many thanks for your help
 

VaughnH

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A drop checker is absurdly simple, so virtually any design works fine. The two critical things are: use distilled or DI water, with a KH of 4 dKH, and not tank water in it, and use a pH indicator that is the bromothymol blue type - yellow at about 6 pH and blue at about 7.2 pH. I think Dennerle's indicator uses the right pH reagent, but I'm not sure if they say to use tank water.

If you are relying on the drop checker it is best to replace the solution in it about every 2 weeks, but some people find it is still good over a month longer. I always found that the indicator dye fades with time, and eventually I couldn't distinguish between the colors unless I replaced the fluid every 2 weeks or so.
 

jonny_ftm

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Mar 5, 2009
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Many thanks for the clarificatiom,

Dennerle system uses an "all rady liquid" that I have to add in the drop checker and it is not mixed with the tank water. So I assume it is fine

I also was replacing 1x/month instead of the Dennerle 1x/15 days recommended. I'll monitor closer if I should shorten teh delays.

many thanks again for your help
 

Nos

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Mar 13, 2009
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Hi,
I'm trying to make 4 dKH solution for my drop checker. I've followed the instructions and according to my test I have 4 dKH solution. Now the only problem that I have is that I cannot make it blue when I add into my drop checker. It always becomes green. I've tried 3 different PH reagents but it always is green. Am I doing something wrong?
 

VaughnH

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Does the color card for the pH test kits you used have yellow for about 6.0 pH and blue for about 7.2 pH? If so, that is the right reagent. It could be that the water you are putting in the drop checker has a pH of 6.8 or less. Are you using distilled water?
 

Nos

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Mar 13, 2009
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Yes the reagent has yellow, green and blue. I’m using RO water so PH will be low(I think 5.8). What water should I use?
 

VaughnH

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The KH standard water has to be both RO and DI (deionized), or it can be distilled water. The goal is to have nothing in the water that affects the pH except carbonates.
 

herns

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Jul 29, 2007
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This is a very informative old thread.

Some ebay Hongkong sellers sells drop checkers that has an instruction to add aquarium water after putting in the CO2 Test Regent that comes with it. Is aquarium water desirable?
 

pat w

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Nov 4, 2009
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I may be able to help here.

First as Hoppy stated in post #42 No Tank Water. You just can't be sure the KH is strictly from carbonate and therefore your results will be inconclusive. Reference 4dKH solution only (5dkh maybe if you want to push your CO2 past 30ppm).

Second, dry your baking soda in a 325 deg F oven for about an hour or so. That temp is important because at around 395 or 396 or somewhere thereabouts the stuff will turn to sodium carbonate and the recipe is no longer valid.

I live on the gulf coast and my first time out I didn’t and got the same results, greenish blue in the drop checker off the bat. This is indicating, I believe, that the KH is under 4d. Unless you live in a seltzer water plant the drop checker should be blue right after you add the reagent.

It was moisture in the baking soda. When I weighed it out, part of that weight was water not sodium bicarbonate. After I dryed it everything worked out like it should have.

Hope this helps.
Pat
 

Left C

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Sep 26, 2005
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Using tank water with the bromothymol blue indicator solution in a dry checker just measures the pH level of the aquarium.

But, using the dKH solution that is carbonate based with the bb solution not only measures the pH, but it lets you get a good estimate of the CO2 level.



Chuck’s CO2 calculator said, “NOTE: This calculator will only work if your water is using is a carbonate buffered. If your water contains high levels of phosphates, it will alter your water properties, and invalidate these CO2 calculations.”

If you have read Chuck's CO2 chart/calculator and he mentions that this chart is only valid if the only buffers are carbonate based. This means that you really can't use aquarium water because it also contains other buffers like phosphate plus other buffers, bases, and acids.

It was hoppy/Vaughn, T. Barr and others that worked this out.

They put 2 and 2 together.

CO2 indicators and Chuck's CO2 chart have been around for many years.

CO2 indicators' directions say to use aquarium water, but they come with the Bromothymol Blue freshwater low range pH indicator.

Chuck's CO2 chart says that it is only valid if you have carbonate based buffers and it also says that with a 4 dKH and a pH of 6.6 that you have 30 ppm of CO2.

Bromothymol Blue works in a pH range from 6.0 to 7.6. It's a yellow color at a pH of 6.0 and lower, a blue color at a pH of 7.6 and higher, and halfway it is a green color.

200px-Bromothymol_blue_colors.jpg


API's freshwater low range pH test kit uses Bromothymol Blue and it's color card shows a greenish color with a pH range from 6.4 to 6.8.

pHcolorcardtestkitAPI.jpg


Then it was decided to make a known 4 dKH carbonate based solution using distilled water. This indicates a green color in the CO2 indicator at a pH of 6.6 for a 30 ppm CO2 level. (There's a little ± in this.)

Presto! They have invented a easy and cheap method to determine the CO2 levels in aquariums reliably with just a simple glance at the aquarium.

I thank them for their hard work. This is a great idea!!

I made my own 4dKH solution by following Bill's directions: http://www.plantedtank.net/forums/general-planted-tank-discussion/42429-kh-standard-how.html

Here's some baking soda/KH/pH calculators and info:
http://dataguru.org/misc/aquarium/calKH.asp
http://www.cnykoi.com/calculators/calckh.asp
http://fins.actwin.com/aquatic-plants/month.200612/msg00109.html
http://jdieck1.home.comcast.net/~jdieck1/chemcalc.html
http://americanaquariumproducts.com/AquariumKH.html
 

anda

Junior Poster
Jul 17, 2010
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Montreal
I have been trying to find a source of premade 4dkh solution but the links on this thread are not functional anymore. I don't have a scale precise enough and I would rather buy it provided the cost is reasonable.

Anyone has a source I can order from?

Thanks!
 

anda

Junior Poster
Jul 17, 2010
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Montreal
Thanks!

I tried the trial and error method with my test kit and got a 4 dkh solution (as per the kit) after a few tries...
 

billypete

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Mar 11, 2009
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Excellent thread !! Just bought 4dkh solution from Aquaessentials :) after spending £14.99 on a jbl drop checker that doesn't show anything other than yellow unless above 7.3 !! Why the hell do they make co2 drop checker kits that don't correctly measure co2 !! Thanks All !!
 

Tom Barr

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Jan 23, 2005
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I still do not like this method.
I cannot tell, nor can many, the difference of .2pH units or often 0.4 or more even.

See how much difference in CO2 that error range is on a pH/KH/CO2 chart.


Regards,
Tom Barr
 

billypete

Junior Poster
Mar 11, 2009
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Tom Barr;55630 said:
I still do not like this method.
I cannot tell, nor can many, the difference of .2pH units or often 0.4 or more even.

See how much difference in CO2 that error range is on a pH/KH/CO2 chart.


Regards,
Tom Barr

Hi. Do you mean with the diy 4dkh or the 'calibrated' solution I've bought ? or both !