KH And CO2 Not Matching Up? - The Planted Tank Forum
 
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post #1 of 11 (permalink) Old 02-02-2013, 06:31 PM Thread Starter
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KH And CO2 Not Matching Up?

So I'm a little confused. I been look at these KH/CO2 charts online and thought it could help with my low CO2 levels. I have a pressurized CO2 tank controlled by a PH monitor that I keep on all the time. My PH is set to 6.6-6.7 and my KH is 5. According to all the charts I should have a perfect CO2 levels but everytime I look at my drop checker is always a blue/green. The picture is of the closes my drop checker every comes to being dead on. And as a side not I just cleaned and changed the drop check solutions a week ago. Thanks for a the help
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post #2 of 11 (permalink) Old 02-02-2013, 07:19 PM
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This is an old pic showing a timeline of DC color change as levels increased in my tank. I don't use one anymore, but I aimed for 12pm color at lights on back then.

Don't be scared of Co2, it's really not that scary as most think it is with all the fish gonna die drama Increase levels IMO.

I never lost a fish from high Co2 either. Make small changes and monitor and adjust again as needed for optimal levels. When you find the sweet spot don't mess with your needle valve settings.





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post #3 of 11 (permalink) Old 02-02-2013, 07:25 PM
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If you are looking at the kH/pH/CO2 chart and the values do not add up use the drop checker as the best reference. You don't have enough CO2 in the water as the drop checker is blueish.

pH may fall as nitrifying bacteria oxidizes ammonia or nitrites and the chart does not account for that. Tannins and other organic acids in the water may eat at you kH and the chart does not account for that also.

All in all, don't use it, it's not accurate. Rely on your drop checker to set the required concentration of CO2 you wish to achieve
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post #4 of 11 (permalink) Old 02-02-2013, 10:04 PM
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Originally Posted by danielt View Post
If you are looking at the kH/pH/CO2 chart and the values do not add up use the drop checker as the best reference. You don't have enough CO2 in the water as the drop checker is blueish.

pH may fall as nitrifying bacteria oxidizes ammonia or nitrites and the chart does not account for that. Tannins and other organic acids in the water may eat at you kH and the chart does not account for that also.

All in all, don't use it, it's not accurate. Rely on your drop checker to set the required concentration of CO2 you wish to achieve
A drop checker is better than the pH/KH table, but it, too, isn't very accurate. It is very difficult to "read" the color of the 4 dKH water to say it is truly green and not yellow green or blue green. Just a small error makes a big difference. If you treat the drop checker as a way to get the CO2 bubble rate up into the ballpark for optimum concentration, then slowly raise the bubble rate, a tiny bit every few days, while observing the plants and fish, you can get much closer to the optimum bubble rate.

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post #5 of 11 (permalink) Old 02-03-2013, 12:26 AM Thread Starter
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I just got home from work and my lights have been on for 7 hours. I'm getting a bubble or two of pearling on my HC here and there. The drop checker looks the same. I'm at two bubbles per second on my co2 tank. How much should I increase the bubbles by and how long should i wait to increase it again if I'm not at my desired level. Not looking for exact numbers just a ball park of what you would do. And Thanks for all the replies
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post #6 of 11 (permalink) Old 02-03-2013, 01:18 AM
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Your kH and pH in your tank is not a good indicator of CO2. They vary due to other factors like water change, substrate, driftwood, rocks, etc... SO relying on the pH controller is by no means perfect (you'd have to recalibrate very often). People have been using it forever but it doesn't make it correct.

You can check out my DIY CO2 sensor controller project. That is pretty accurate but you're right; a ball park number is fine.


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post #7 of 11 (permalink) Old 02-03-2013, 02:26 AM
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This is a huge misconception. I've seen the chart, and most people think that this is for their tank water, as is. That is FALSE. For this method, you take tank water out, measure KH and pH, wait 24 hours, then measure it again. After a day most of the CO2 will leave the water into the air, so the difference in pH should tell you something about how much CO2 you had.


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post #8 of 11 (permalink) Old 02-03-2013, 05:01 AM
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This is a huge misconception. I've seen the chart, and most people think that this is for their tank water, as is. That is FALSE. For this method, you take tank water out, measure KH and pH, wait 24 hours, then measure it again. After a day most of the CO2 will leave the water into the air, so the difference in pH should tell you something about how much CO2 you had.
And, this method is also inaccurate. It gives you some information about the ratio of ppm of CO2 for the water in the tank, and the water after it sits for 24 hours. But, you don't know how much is in the water after it sits for 24 hours, so the ratio doesn't let you determine what it was before the 24 hour sit. We like to see a rise in pH of 1.0, meaning there is only one tenth the ppm of CO2 that was there before it sat for 24 hours. Then people have assumed, without ever verifying it, that the water will always have 3 ppm after sitting for 24 hours, so that 1.0 rise in pH means it started out at 30 ppm. But, I did some testing and found that the ppm of CO2 in the water after 24 hours could vary considerably, and the ppm kept dropping for at least another 24 hours.

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post #9 of 11 (permalink) Old 02-03-2013, 05:05 AM
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I'm more inclined to have folks suggest the pH/KH table, then slowly ...........and like 1/20th of a turn of the needle valve each step, adjust it up from there and watch the tank closely.

We cannot say that 15ppm or 30 ppm is optimal, each tank will be different.
My tanks sit at 70 ppm and 55 and 50 ppm.

I adjust slowly and watch the plants, and the fish etc.
As long as I get more plant response and the fish are fine, I will add more.
I have good current and surface movement and high O2 levels.

So this counter acts any issues with high CO2.

My tap water has a KH of 1 degree or about 20 ppm.
So even if there's other non carbonate alkalinity in that number, it AIN"T much.

If you have a higher KH's, say 4-10 degrees etc, then you have a lot of potential room for errors in the assumption that it is all carbonate alkalinity.

This might be another advantage soft water users have.

I also use the volume per minute of CO2 to adjust things.
I bubble the CO2 into a large clear container, then time how long it takes to fill say 500mls, or some known volume. A measuring cup can work.

Then If I suspect anything changed, I can always use that as a reference.
the rate of CO2 will always be a stable reference, independent of the KH or pH, or drop checkers etc.

And it's free/cheap, easy to do.

I needed to change my old regulator for a new dual stage and wanted the same rate of CO2, this allowed me to do ti easily without having to go through the process of readjusting and watching for weeks to dial it in.

Dry ice, a sealed container with a pH probe rubber gasket sealed port and some reference KH solution can make a CO2 ppm water reference solution also.
Also, do not use the pH controller except for the day time only(eg, with the light timer).




Regards,
Tom Barr

Last edited by plantbrain; 02-03-2013 at 05:05 AM. Reason: cuz
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post #10 of 11 (permalink) Old 02-03-2013, 05:53 AM Thread Starter
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thanks for the help everyone
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post #11 of 11 (permalink) Old 02-03-2013, 09:22 AM
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One thing to add, increasing slowly the CO2 rate allows your creatures to adjust to your levels and you will be able to raise the levels higher than otherwise possible.

Be weary of going overboard with the water acidity as molluscs and crustaceans will have difficulties in maintaining their shell integrity if not enough calcium and minerals are present in their diet.
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