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Here's a calculator:

http://www.fishfriend.com/aquarium_co2_calculator.html

As always, the output is highly dependent on the accuracy of the input. Try bumping the KH up or down one degree, and you'll see what I mean. A KH test kit only gives you results to the closest degree, and it's easy to read pH wrong by 0.2, so some error is expected.

Plus if there's non-carbonate alkaline buffers in your water, that will completely throw it off too. Though this isn't usually the case.

This is why a drop checker is preferred.
 

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Is a drop checker basically accurate no matter the KH of the tank or is it also dependent on that?
A drop checker will react to the amount of CO2 that gases off from the water. kH will change that amount, as it affects how much CO2 you have in the water. That's why pH does not drop under a certain value depending on how high is the kH.

So, the drop checker is accurate but slow. It will show your CO2 level about 30 minutes to an hour ago. Not the current value.
 

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A drop checker will react to the amount of CO2 that gases off from the water. kH will change that amount, as it affects how much CO2 you have in the water. That's why pH does not drop under a certain value depending on how high is the kH.

So, the drop checker is accurate but slow. It will show your CO2 level about 30 minutes to an hour ago. Not the current value.
So are you saying that a high KH requires more CO2 in the water but the drop checker still accurately reflects that. Green is green and yellow is yellow.
 

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So are you saying that a high KH requires more CO2 in the water but the drop checker still accurately reflects that. Green is green and yellow is yellow.
KH has no effect on the amount of CO2 required. It only affects how much a certain amount of CO2 changes the pH. More KH, less change; less KH, more change.

A drop checker is really just a pH tester. Only CO2 can enter. Water cannot, and because the water inside always has a fixed and known KH, it always produces a predictable color change for a certain amount of CO2.
 

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KH has no effect on the amount of CO2 required. It only affects how much a certain amount of CO2 changes the pH. More KH, less change; less KH, more change.

A drop checker is really just a pH tester. Only CO2 can enter. Water cannot, and because the water inside always has a fixed and known KH, it always produces a predictable color change for a certain amount of CO2.
That explains it well. Thanks.
 

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To convert ppm to more familiar degrees, divide by 17.86. Which, rounded to one decimal point, gives you:

gH=10.1 (hard)
kH=6.7 (plenty high enough to keep the pH from dropping too low with CO2)
 

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I used an AP pH test strip and if i have 120ppm kH and 180ppm gH is that considered hard water and good for plants when using co2??
Depending on the plants. If you have soft water plants that is too much. You might want to target a kH of 3-4 dkH and gH of 6 or lower dgH.

dmagerl said:
I dont think it even does that. A 1 point drop in ph is always a 10 times increase in CO2 regardless of KH.
kH will determine how much CO2 stays in the water as carbonic acid. There are separate reactions when it comes to CO2.

Plants use CO2, part of it will react with water and make carbonic acid, a huge part of this acid will "decompose" further into bicarbonate giving off an Hydrogen ion thus making the pH go down. Adding bicarbonate into water will slow the carbonic acid from breaking down and cause a pH drop. More carbonic acid will form and the CO2 concentration in the water will drop. Lower kH will allow the reaction to carry on, bicarbonates further "decompose" into carbonate and another Hydrogen ion is released. Finally, carbonate itself breaks down into water and CO2.

It's hard to describe exactly how much CO2 you have in the water at any given moment. That is because the reactions that take place are pH, temperature and kH dependent. This is the reason why you want a low kH in a planted tank.
 

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Discussion Starter · #15 ·
This maybe a stupid question but does adding fertilizers to the water column raise gH and kH??
Reason i'm asking is because, I was going over my EI dosing using the nutrient calculator from http://calc.petalphile.com/non-mobile
and i think i may have to up the ante on my dosing I don't think i'm adding enough.
Im using the macro and micro pack from Green Leaf aquariums
the pack comes with
Micros -
Plantex CSM + B - 1 / 2 Pound
Macros -
Potassium Nitrate (KNO3) - 1 Pound
Mono Potassium Phosphate (KH2PO4) - 1 / 2 Pound
Potassium Sulfate (K2SO4) - 1 Pound
but when i got this pack i read to add about 1/8 teaspoon of each macro in 60ml distilled water and mix and dose about 1-2ml of that mixture to my tank about 1-2 times a week.
am i doing anything wrong?
 

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danielt, I agree with what you say, but if you look at that co2/ph/kh table, no matter what kh you start at, a 1 point drop in ph is always a 10 times increase in CO2. So if kh really affects CO2 concentration per ph drop, that table is really really screwed up.

Also, based on my experience, regardless of KH, my drop checker always gives the same green shade for the same ph drop. So if KH really affects the chemically available CO2 in the water column, a drop checker isnt really a good way to measure CO2 percentage, eh?
 

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Seems you got it right :D

The table is pretty much useless in practice. I had this discussion with some of my fellas on other local forums. Mathematically, the table is correct, it will show you accurate values if you do the math.

If pH will vary ONLY because of kH and the kH will not vary unless CO2 is added, the table would be useful. In reality, you just need a filthy tank to screw the table ;)

The drop checker will be accurate as it will show you what gasses off. However, you might need, for example, 3 bps in some cases to make it yellow or just 1.5 bps in others.

Just because of that, one telling you how much CO2 is dosing doesn't mean much unless they keep the drop checker at a constant colour.

It is wrong to assume or compute anything from anything when it comes to CO2. The drop checker uses a reference solution that's not affected by changing conditions in your tank. The problem arises when you look at the drop checker and establish a pH or kH value by referencing the drop-checker's colour. That's inaccurate/unreliable.
 

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Discussion Starter · #18 ·
I have pretty hard water, so gH I should not have to worry about, just monitor my kH and pH? correct?
I currently only have the pH strips to check, would a drop checker be better to keep an accurate reading of co2 than bps?
 
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