Electronic Drop Checker - The Planted Tank Forum
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post #1 of 3 (permalink) Old 01-14-2010, 09:45 PM Thread Starter
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Electronic Drop Checker

I've been studying up on CO2 systems and how CO2 concentration is measured with a PH probe and drop checker and the associated pros and cons of each method and I was struck by a idea that seems like it would give the best of both worlds: Build a drop checker but rather than using an indicator in the 4dkh solution, stick a PH probe in there instead. Something like the attached image...

This way you get the best of both worlds. Your test solution won't be affected by fertilizers and other additives or tap water condition, and you PH probe will be isolated from the biofilm buildup and other contaminants that cause them to degrade over time. You also get a more precise reading than a drop checker alone could provide. The only downside I can see to this method is that it's going to be a lot slower sensing changes than a PH probe in the tank (but no slower than a normal drop checker).

Has anybody done this before? Any thoughts?
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post #2 of 3 (permalink) Old 01-15-2010, 12:20 AM
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This was suggested before, I believe, but I can't seem to find the thread right now.

Also, do note that for the current way you have drawn your schematic, the pH probe should be more completely submersed in liquid in order to maintain its longevity.


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post #3 of 3 (permalink) Old 01-15-2010, 03:22 AM
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This will definitely work. But, the reaction time for a drop checker increases as the volume of fluid in it increases. It also increases as the area of that fluid exposed to the gases from the tank water decrease compared to the volume of the fluid in the bulb. This means to avoid a very, very slow acting device you need a very small pH probe, and those tend to be expensive.

The two biggest problems with a drop checker are the uncertainty in pH caused by having to judge the color of the solution, and the very slow response time. This type of drop checker corrects one problem but makes the other one worse. Another problem with any method for measuring CO2 in the tank is that the concentration of CO2 in the water varies all over the tank. It can be very low near the plants and very high near the filter return, where the CO2 is introduced. This makes it virtually impossible to get one measurement in a tank and expect that to be typical for the whole tank.

A drop checker is very good for giving you the courage to increase the bubble rate until you finally get near the optimum amount in the water, but I doubt that it will ever be good for finding a good reading of what the average ppm of CO2 in the tank water is.

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