PH probe and drop checker question - The Planted Tank Forum
 
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post #1 of 6 (permalink) Old 04-25-2008, 02:38 AM Thread Starter
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PH probe and drop checker question

Can somone explain why a ph probe and a drop checker give completely different results when measuring C02? My ph probe is well calibrated and the drop checker has a carefully prepared 4dkh solution. kh is 2.5, the ph probe reads 6.2 with a theoretical c02 level of 47.3 ppm but the drop checker is bluish green indicating a lower c02 level. Isn't the drop checker basically just another way to check ph??

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post #2 of 6 (permalink) Old 04-25-2008, 02:40 AM
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Have you used any buffers on this tank? That will throw off some measures, espeically that pH/kH/CO2 chart...





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post #3 of 6 (permalink) Old 04-25-2008, 02:46 AM Thread Starter
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I use a gh booster. My water is very very soft.

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post #4 of 6 (permalink) Old 04-25-2008, 03:34 AM
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Hi calihawker

GH Booster has no effect on the drop checker.

A drop checker is basically a freshwater low range pH test kit made with Bromothymol Blue indicator solution and a known 4 dKH solution made from baking soda and distilled water placed inside the aquarium using a drop checker.

The drop checker is green when the solution inside it reaches a pH of around 6.6 indicating a 30 ppm CO2 level. Please note that there is some in this

The drop checker works independently from the aquarium water pH and KH because of the air gap that allows the gas exchange and the two different "waters" don't mix. It's only measuring the CO2 level. As long as your drop checker is green using proper 4 dKH solution, you have a safe CO2 level for the critters and a good CO2 level for the plants. Bromothymol Blue indicator solution is CO2 sensitive.

Don't use the pH/KH/CO2 chart/calculator for calculating your CO2 level using aquarium water. There can be errors from poor quality test kits and there's plenty of phosphates, other buffers, acids, bases, tannins, etc. that usually skew the results to the high side. The pH/KH/CO2 relationship chart/calculator only works if the only buffers are carbonate based. Go back and read Chuck's chart/calculator article about this.

I have pH controllers on my aquariums and I have very soft water. I have to set the pH controllers at 6.2 to get a good green color.

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post #5 of 6 (permalink) Old 04-25-2008, 04:13 AM Thread Starter
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Now I get it. The solution in the drop checker has nothing to do with the aquarium water.

Left C, let me ask you this, since you use a controller as well. Do you set the controller and let it run day and night? That's what I've been doing and then run a small pump at the surface at night for O2.

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post #6 of 6 (permalink) Old 04-26-2008, 06:02 AM
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I'm sorry, but I missed your question, calihawker.

The drop checker with the known carbonate based dKH solution is a very profound recent equipment addition to our hobby/job, IMO.

I run my pH controllers 24/7. I tried hooking up the solenoid power cord to a timer one time so that it would be off when the lights are off. I never saw any difference between running it 24/7 or only on when the lights are on. It makes sense that you would use less CO2 by doing this though.

I don't see any problem adding air when the lights are off. Most plants and animals use O2 24/7 just like we do. You might use a little more CO2 this way unless you cut it off when the lights are off.

Just remember that water can be 100% saturated with O2 and 100% saturated with CO2 independently from each other.

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