Question About Co2 Drop Checker - The Planted Tank Forum
 
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post #1 of 6 (permalink) Old 09-07-2012, 03:39 PM Thread Starter
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Question About Co2 Drop Checker

It is my understanding that a Co2 drop checker uses the Ph/Kh realtionship. My drop checker is showing green (it was blue for a while). I haven't done anything different, except lower Kh and Ph. My question is, would this affect the drop checker? Does lower ph/kh mean higher Co2 in all circumstances? If a drop checker only measures the ph and kh, and a lower ph/kh doesn't necessarily mean higher Co2, how can you trust it?
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post #2 of 6 (permalink) Old 09-07-2012, 04:38 PM
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All the drop checker is is a permanent pH check. You load it with a few drops of 4 KH water plus a drop or two of pH test solution. If the pH drops the color in the drop checker moves towards yellow. If the pH rises the color moves towards blue. It can take a couple hours for the color to change depending on the water movement at the drop checker's water surface.

The CO2 chart is based on the relationship between pH and KH. If KH drops and pH stays the same because CO2 is introduced then there is more CO2 in the water. If KH drops because you put in a KH absorbing substrate or peat then there isn't any more CO2 in the water than before. That is why we use 4 KH water in the drop checker, so variables in tank water don't lull us into complacency about having plenty of CO2 because the pH is this and the KH is that.


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post #3 of 6 (permalink) Old 09-07-2012, 05:10 PM Thread Starter
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So is a drop checker pretty much worthless?
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post #4 of 6 (permalink) Old 09-07-2012, 06:30 PM
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If you have a pH monitor than yes. If not it's a valuable tool to hone in the correct CO2 level.


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post #5 of 6 (permalink) Old 09-07-2012, 07:07 PM Thread Starter
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So if I have low ph levels and low kh levels, does that mean I have high Co2 levels? I'm just trying to understand how all of this works...
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post #6 of 6 (permalink) Old 09-07-2012, 10:51 PM
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Quote:
Originally Posted by Kathyy View Post
All the drop checker is is a permanent pH check. You load it with a few drops of 4 KH water plus a drop or two of pH test solution. If the pH drops the color in the drop checker moves towards yellow. If the pH rises the color moves towards blue. It can take a couple hours for the color to change depending on the water movement at the drop checker's water surface.
This isn't at all true. The water in the drop checker is pure water, except for having enough sodium bicarbonate in it to raise its KH to 4 degrees. Then 2 or 3 drops of API pH reagent, or equivalent, is added so the color of that water will reflect the pH of that water, not the water in the tank. As CO2 is added to the water in the tank it migrates into the drop checker water too, at the same concentration as in the tank, changing the pH and color of that water. If the tank water KH changes it has no effect at all on the drop checker color. The time it takes for the drop checker color change to occur is dependent on the surface area of the drop checker water that is exposed to the trapped air in the drop checker, on the surface area of the air to tank water interface, and the volume of air and water in the drop checker. To get rapid response takes low volume of water in the drop checker, large contact area of that water to the air in the drop checker, small volume of air in the drop checker, and large contact area between the air in the drop checker and the tank water.
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The CO2 chart is based on the relationship between pH and KH. If KH drops and pH stays the same because CO2 is introduced then there is more CO2 in the water. If KH drops because you put in a KH absorbing substrate or peat then there isn't any more CO2 in the water than before. That is why we use 4 KH water in the drop checker, so variables in tank water don't lull us into complacency about having plenty of CO2 because the pH is this and the KH is that.

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