Problem determining co2 from KH and PH readings - The Planted Tank Forum
 
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post #1 of 8 (permalink) Old 06-15-2008, 06:59 AM Thread Starter
 
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Problem determining co2 from KH and PH readings

I've been using a drop checker and KH and PH readings to determine co2 levels. The drop checker (Red Sea) is light green and seems to be working correctly. I've seen it go to yellow when I made too strong a batch for my DIY fermentation canister and my fish gasping for air before . I've also seen it blue when the fermentation stopped. So I tend to believe I have the right level of CO2

I use two different KH and PH test kits which read consistently against each other, and read 10 degrees KH and PH of 6.6. If I read charts correctly, that would be 75 ppm.

My fish and cherry shrimp are thriving, the cherries are breeding and some young have grown to adults.

I use deionized water (API Tap Water Filter) remineralized with ElectroRight for water changes. KH reads 3 when I put it in the tank. But the tank always reads 10.

I don't use Peat, and I don't use PH adjusters. Phosphates read less than .25 ppm. I also use eco-complete as my substrate.

I can't make sense of this,

1) do the KH and PH readings make sense? Wouldn't a CO2 concentration of 75 ppm kill my fish and cherry shrimp?
2) What is likely driving the KH up?
3) Should I try to keep the KH lower? How?


Thanks
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post #2 of 8 (permalink) Old 06-15-2008, 03:09 PM
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I've read that using kH buffers will cause the CO2 chart to be inaccurate. I use this calculator http://www.fishfriend.com/aquarium_co2_calculator.html , and it states:

This calculator is only accurate if no phosphate buffers such as pH-Up, pH-Down and Discus Buffer is present.

So I don't think you really have 75ppm CO2.
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post #3 of 8 (permalink) Old 06-15-2008, 03:13 PM
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I've read that some substances like tannins can adjust your pH to the point where the pH/KH/CO2 relationship is off. Verifying that your tank adheres to the chart would be my first step. Measure pH/KH after the tank has been idle without CO2 injection for 24hours(longer if you don't have much surface current). Never had shrimp before, but would it be bad to stop CO2 for a day so you can get a reference? I have eco also and my KH & PH increased after I put it in. My KH went from 2 to 6, so 3 to 10 doesn't sound too unreasonable.

How long has the tank been set up? Your KH may settle down after some water changes if it's new. Also, I've never used Electro-Light, I guess it's a GH booster but verify that it doesn't boost KH also. You can just add some to a test sample and measure KH before and after. I would tend to trust the drop checker more than anything until you figure out your water parameters.
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post #4 of 8 (permalink) Old 06-16-2008, 03:40 AM Thread Starter
 
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Thank you both for the advice. The comment about tannins makes me wonder - I have some malaysian driftwood and that would contain tannins right? That would explain the kh/ph/co2 relationship not making sense.

On the Electro-right, after using it, the water is 3 degrees kH. I will turn off the co2 injection as suggested and see what the readings are.

I have used ph-down, but not for a long time, and it has been many water changes ago. Tha tank has been set up for more than 4 months.
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post #5 of 8 (permalink) Old 06-17-2008, 09:48 AM
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are you filling the drop checker with tank water?

or a 4DKH solution? it just seems odd that a single diy co2 (even a strong batch) would put it up high enough to go yellow.

if you had 4dkh in your checker you wouldnt need to worry about the kh/ph chart.

dont wanna buy 4dkh? dont wanna make 5 liters with a graduated cylinder and a triple beam either? neither did i. i made it the easy way.

you already have a kh test kit.. since we need the kh at 4 degrees go to the store and pick up a jug of DISTILLED water and some baking soda (if you dont already have some..) then get 2 cups. pour each half full distilled water.
then put a good pinch of baking soda in one of them. stir well and give time to dissolve. then pour this into the other cup, a little at a time. test it repeatedly until 4 drops turns it yellow and it's good. then save what's left of this mixture and dump the other.

Discus, (The Other White Meat.)

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post #6 of 8 (permalink) Old 06-17-2008, 11:36 PM Thread Starter
 
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Thanks, I have been using tank water.

If I use the 4 dkh water, do I still read the drop checker the same way? Does green still mean good, yellow too much, etc?

What is this doing when I use this solution?

Quote:
Originally Posted by DiscusIt'sWhats4DinneR View Post
are you filling the drop checker with tank water?

or a 4DKH solution? it just seems odd that a single diy co2 (even a strong batch) would put it up high enough to go yellow.

if you had 4dkh in your checker you wouldnt need to worry about the kh/ph chart.

dont wanna buy 4dkh? dont wanna make 5 liters with a graduated cylinder and a triple beam either? neither did i. i made it the easy way.

you already have a kh test kit.. since we need the kh at 4 degrees go to the store and pick up a jug of DISTILLED water and some baking soda (if you dont already have some..) then get 2 cups. pour each half full distilled water.
then put a good pinch of baking soda in one of them. stir well and give time to dissolve. then pour this into the other cup, a little at a time. test it repeatedly until 4 drops turns it yellow and it's good. then save what's left of this mixture and dump the other.
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post #7 of 8 (permalink) Old 06-18-2008, 02:55 PM
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Steven,

Give this link a read its full of good info...
https://www.plantedtank.net/forums/ge...lp-please.html

You can only accurately get Co2 levels if you are using DK4 solution.. If you change your DK solution to something other than 4 than your Co2 PPM would change as well. once your DK4 solution reads green in your drop checker your at 30 ppm Co2....Simple. all tanks have to many variables effecting PH which will always give erroneous readings... Hence using DK4 is the only way of giving you accurate C02 levels

Troy


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post #8 of 8 (permalink) Old 06-19-2008, 06:02 PM Thread Starter
 
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Thank you all so much. This makes sense to me now.
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