Question Can I use a pH test for CO2?

psalm18.2

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So I've been doing some reading. Seems CO2 drop checkers use 4dKH solution to monitor CO2. Some people even make their own drop checkers. Stick on pH monitors or even pH liquid tests are cheaper than drop checkers. Why can't I just use pH tests to monitor my CO2 level? According to this article, 6.6 pH=30 ppm CO2.

What do you think?
 

catsma_97504

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To use pH to estimate CO2 absorption you need to gas off some tank water to determine the pH of the water itself. Transfer some water to a container with an airstone and test at 24 hour intervals until the pH doesn't change. This is your base pH.

Then, run your pH test as usual in your tank. As pH levels will change throughout the day, you should test it before lights on and before CO2 kicks in, unless using DIY. Compare the difference between the pH readings.

Because pH is a logarithmic algorithm, the only solid landing point is that a 1.0 degree difference in pH equates to 30PPM CO2.

The advantage of having a drop checker is that they continually monitor changes in pH levels to warn you of a potential overdose that could affect fish. Regardless of the vessel used, they are filled with 4 dKH water and the pH reagent.

For me, after the initial investment, I use distilled water and baking soda to make 4 dKH water and add pH reagent to make the mix.

Hope that helps.
 
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psalm18.2

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What ratio of baking soda & regiment do you use? I've heard this can be done.
 

catsma_97504

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With distilled water, I used a 500 ml bottle and the smallest amount of baking soda possible. I literally used my pinky fingernail. Only touched the baking soda with the tip of my nail. And started with 15 dKH! The measurement is so small that I can't tell you how much to use. I then ran a KH test to adjust until I came up with the correct level.

Once you have the correct solution, the place the appropriate amount in the drop checked with 4-6 drops of pH reagent.
 
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psalm18.2

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I've been reading and found an interesting chart. The chart takes pH level and kH level and gives a CO2 level. I know my pH is always 7.6. I have a tester sitting to compare tomorrow. I added more DIY CO2 today.
 

bass master

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KH/pH charts are useful for getting a rough estimate of co2 levels, but I wouldn't trust them any closer than plus/minus 10ppm. The charts assume carbonates are the only thing affecting pH, while there are actually quite a few other factors that have an effect. Personally I've never used anything other then these charts and haven't had any big problems with my co2

-Bass master
 
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psalm18.2

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KH/pH charts are useful for getting a rough estimate of co2 levels, but I wouldn't trust them any closer than plus/minus 10ppm. The charts assume carbonates are the only thing affecting pH, while there are actually quite a few other factors that have an effect. Personally I've never used anything other then these charts and haven't had any big problems with my co2

-Bass master
Until I start using real gas, an estimate is ok.
 

catsma_97504

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KH/pH charts are useful for getting a rough estimate of co2 levels, but I wouldn't trust them any closer than plus/minus 10ppm. The charts assume carbonates are the only thing affecting pH, while there are actually quite a few other factors that have an effect. Personally I've never used anything other then these charts and haven't had any big problems with my co2

-Bass master
You are one of the lucky ones then!

With the high levels of PO4 in my tap water, those charts are useless. When I was using DIY those charts indicated I had over 75PPM CO2. Enough to kill my fish; yet they were healthy, active and breeding. And my tank was overrun with BBA. It didn't add up.

I went crazy trying to estimate CO2 level. I refused to spend $100 on a CO2 test! Using the difference in pH was the only thing that made sense for my situation. This estimate gave me a CO2 level around 15PPM. Huge difference.
 
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psalm18.2

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I have base levels from tap to use for reference. Those drop checkers are so expensive. Is the regent used just pH test kit fluid?
 

bass master

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You are one of the lucky ones then!

With the high levels of PO4 in my tap water, those charts are useless. When I was using DIY those charts indicated I had over 75PPM CO2. Enough to kill my fish; yet they were healthy, active and breeding. And my tank was overrun with BBA. It didn't add up.

I went crazy trying to estimate CO2 level. I refused to spend $100 on a CO2 test! Using the difference in pH was the only thing that made sense for my situation. This estimate gave me a CO2 level around 15PPM. Huge difference.
daggone, never had the charts be that far off, good warning though!
 
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