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Mebbid
Aquarium Advice Addict
Thats why I decided to go with a drop checker. It completely removes the tank water from the equation.
CO2 chart
- Thread starter Mebbid
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Out of interest what is the issue there? Is it past the chart range or the chart is more inaccurate at higher ph / kh or something?
jeffaquarius
Aquarium Advice Addict
The CO2 test kits are calibrated for fresh water with lower pH than salt water.
Caliban07
Aquarium Advice Addict
Dela I could be wrong but I think the chart is accurate because the chart is assuming that the only dictator of ph level is co2. So at X kh with X ph where co2 is the only dictator of ph than co2 will be X with an accurate mathematical equation. The discrepancy comes as soon as you use our tank water. Perhaps that link was saying that our tanks have a tolerance as high as +- 20%
Mebbid is right. You have to use a drop checker to eliminate the discrepancies and the water used is RODI calibrated with a known kh value typically 4dkh? It's in a little chamber which allows co2 gas through a membrane. That way if you know the ph and kh of that water and the only effecting factor is co2 in theory the colour that chamber turns should match that of the chart. Actually measuring a true value is difficult but one has to assume it is what the chart says.
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Mebbid is right. You have to use a drop checker to eliminate the discrepancies and the water used is RODI calibrated with a known kh value typically 4dkh? It's in a little chamber which allows co2 gas through a membrane. That way if you know the ph and kh of that water and the only effecting factor is co2 in theory the colour that chamber turns should match that of the chart. Actually measuring a true value is difficult but one has to assume it is what the chart says.
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Caliban07
Aquarium Advice Addict
All co2 kits? I'm wondering if the manufacturer of the kit I linked do one for saltwater too.
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I found a later thread but it does contain the original thread I was thinking of. At the time I had no co2 injection so any error / test kit bias didn't make much difference. Low co2 was still low so to speak.
Once I flush the buffer out of the tank, I'll see if the chart comes in closer to the drop checker reading.
Edit - and now with link
http://www.plantedtank.net/forums/showthread.php?t=10041#/forumsite/20495/topics/10041
Would the ph/kh/co2 chart still work though as it is basically a mathematical formula?
If it doesn't work, would you know what causes it to be wrong in SW?
This is just for interest to see if the chart is any more reliable in SW. For example I'm assuming driftwood is not commonly added in SW tanks.
OP
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Mebbid
Aquarium Advice Addict
Good article on it that seems to agree with you. http://www.reefkeeping.com/issues/2007-05/rhf/
Also, youre correct driftwood is avoided in reef tanks.
Also, youre correct driftwood is avoided in reef tanks.
Caliban07
Aquarium Advice Addict
The chart does not care what type if water is involved. It is using a specific value of alkalinity. Whether the alkalinity is affected by calcium carbonate or sodium bicarbonate is irrelevant. The equation states that at that particular kh level with this particular ph level (only altered by carbonic acid) the carbon dioxide level will be X. The chart uses that formula right across the board.
When we take the chart across to use in saltwater or freshwater the values become meaning less because the conditions required to get the scientifically and mathematically correct answer for co2 do not exist.
The chart therefore cannot be used reliably in any setup. It is the ph value that really matters though. The chart doesn't care what kind of buffers are present because they all contribute to the measured alkalinity value. What is important is the things that are present that directly alter the ph level. For example, like you say the addition of driftwood. The chart is not taking tannic acid in to consideration during the calculation and it is impossible to subtract the ph difference caused by tannic acid. Tannic acid is just one example, there my be others.
In turn the ph value becomes unreliable for the equation because there are other factors affecting it.
The problem we face is determining kh. How accurate is the kit used for this? Already we have discrepancies and tolerance.
The chart can only be used as a very rough guide as far as I understand.
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Mebbid
Aquarium Advice Addict
The higher end test kits are quite accurate for measuring dKH. The red sea kit I use for example is accurate within 0.14dKH which for all intents and purposes would allow for a margin of error that's not going to harm anything.
Caliban07
Aquarium Advice Addict
I agree the margins will be tiny. Then there's the ph test kit. Then there's the accuracy of the drop checker.
Ideally you would want to measure co2 of the solution inside the drop checker to see how close this is to the calculation. And even then there would be a tolerance on that kit. I know that these tolerances would probably be tiny.
It would be very difficult to prove the calculation even with high end kit and known values. To use the chart with unknown values decreases reliability significantly.
I'm not trying to be clever or anything here and I hope I'm not coming across that way. I agree a drop checker is by far the best way to go and your checking for colour at the end of the day of which there is a fairly wide limit on anyway.
How often do you have to change the solution in the drop checker? Id imagine fairly regularly to maintain a degree of accuracy?
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The fluval drop checker I have now says every 2 to 4 weeks for changing the liquid. Only been using it for one week so not sure what happens to the colour when it stops working. The drop checker has a round sticker (right side of box in link) which basically has ok, low and high. From reading "ok" (green) is 25 to 35ppm roughly. So not the greatest accuracy it seems. And of course I can't really tell the green shades either. But it will annoy me if the chart says one thing and the drop checker says another and I can't explain why or put it down to error. At the moment they disagree by ~15ppm.
http://www.amazon.com/Fluval-A7551-CO2-Indicator-Kit/dp/B0052M9886
From post #31 of link below. From reading below it does seem that at higher ph values the chart becomes invalid. I "think" I have read somewhere that this is the case with kh as well. At low ph and kh (all else being correct), the chart is more likely to be correct.
"KH kits measure HCO3, CO3, and other pH - resisting buffers. At a pH lower than 8.32, ~100% of the carbonate buffer system is HCO3 and little CO3 exists. So CO3 is eliminated, which is a good thing. This means at a pH higher then 8.32, the chart is invalid since our KH kits are affected by both CO3 and HCO3 - we only want HCO3. The same logic applies if we have a lot of other non-carbonate buffers, which influence KH and make it appear we have more HCO3 than actual."
The PH-KH-CO2 equation completely wrong? UPDATE on 22nd post - Page 3
I guess where I'm trying to get to is understanding what makes the chart work or not work (while leaving the chemistry to the experts lol). For example over summer here the tap ph and kh tends to be lower. Over winter it climbs so I could just see myself finally being happy and then get a tap ph of 8.4 which mucks up the chart (as a rough example of Murphy's Law in my tank).
http://www.amazon.com/Fluval-A7551-CO2-Indicator-Kit/dp/B0052M9886
From post #31 of link below. From reading below it does seem that at higher ph values the chart becomes invalid. I "think" I have read somewhere that this is the case with kh as well. At low ph and kh (all else being correct), the chart is more likely to be correct.
"KH kits measure HCO3, CO3, and other pH - resisting buffers. At a pH lower than 8.32, ~100% of the carbonate buffer system is HCO3 and little CO3 exists. So CO3 is eliminated, which is a good thing. This means at a pH higher then 8.32, the chart is invalid since our KH kits are affected by both CO3 and HCO3 - we only want HCO3. The same logic applies if we have a lot of other non-carbonate buffers, which influence KH and make it appear we have more HCO3 than actual."
The PH-KH-CO2 equation completely wrong? UPDATE on 22nd post - Page 3
I guess where I'm trying to get to is understanding what makes the chart work or not work (while leaving the chemistry to the experts lol). For example over summer here the tap ph and kh tends to be lower. Over winter it climbs so I could just see myself finally being happy and then get a tap ph of 8.4 which mucks up the chart (as a rough example of Murphy's Law in my tank).
Caliban07
Aquarium Advice Addict
What alkalinity level are you using to cross reference on the chart?
How did you conclude that the measures level on the drop checker deviates by 15ppm?
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As far as I can tell from the fluval drop checker instructions the indicator solution is premixed already. I can just read the solution colour once setup. This has a time delay of an hour or two so not an instantaneous reading.
When I set it up the colour was initially dark blue and then went to green with a yellow tinge. Which seems to be around 30ppm.
Example link below has a co2 reference to the colours.
http://aquatic-art.blogspot.com.au/2011/02/drop-checker-in-planted-aquarium.html?m=1
When I set it up the colour was initially dark blue and then went to green with a yellow tinge. Which seems to be around 30ppm.
Example link below has a co2 reference to the colours.
http://aquatic-art.blogspot.com.au/2011/02/drop-checker-in-planted-aquarium.html?m=1
Tank ph is say 7 to 7.1 and kh is around 4.5 to 5. Which appears to give around 15ppm CO2 from chart? Thus a difference of 15ppm or so to drop checker?
The ph is measured continuously with a ph meter which is fairly new and was calibrated on setup. I have checked with a hand digital ph meter and fairly close.
Kh is just from API liquid test kit.
The ph is measured continuously with a ph meter which is fairly new and was calibrated on setup. I have checked with a hand digital ph meter and fairly close.
Kh is just from API liquid test kit.
jeffaquarius
Aquarium Advice Addict
In salt water aquarium the stability of pH is the indicator of acceptable levels of oxygen and CO2. If it fluctuates too much like about 0.2 (edit:during the day) then you have a CO2 problem.
Caliban07
Aquarium Advice Addict
What Is the premixed reference solution dkh?
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That's the trouble - it doesn't say. Will post instructions tonight in case I'm stuffing up but will email them as immensely confused now. Ruddy frustrating .
OP
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Mebbid
Aquarium Advice Addict
If it's a premixed solution it's gonna be 4dkh.
Caliban07
Aquarium Advice Addict
Well in order to verify the accuracy of the drop checker you would have to read the chart at the same dkh.
The other thing is, the drop checker is using a substance "something blue" can't remember to check ph. It knows that the only influence on ph is carbonic acid and it knows the dkh value (again calibrated at source). Using these 3 it can estimate the ppm of co2.
So you have discrepancies with 2 different measuring methods of ph 1. Your machine 2. The blue substance in the drop checker.
Then you have the accuracy of the premixed solution calibrated at source.
The chart is also a real time value whereas the drop checker is not real time. This creates another host if potential inaccuracies. This bodes the same when measuring c02 of patient expired gas. There are two types of measuring 1. Main stream 2. Side stream. Mainstream is real time because the sensor is located inline with the intubation tube whereas side stream pulls a sample from the main line to a sensor located elsewhere so the information fed back is a) behind and b) is open to all kinds of other factors which may affect readings such as pressure, temperature etc.
Also the drop checker colour indicator has a 10ppm variation between each colour so there is huge room for inaccuracies there too.
When I say inaccuracies I don't mean that the drop checker is a null method, what I mean is, it can't be easily compared to a real time calculation.
At the end of the day without spending probably thousands of pounds we are limited to low end methods of co2 measurements and the drop checker is accurate to whatever the manufacturers specifications are and the user as far as they are concerned should only be interested in the colour. To me your checker is telling you you have high co2 at a dkh of 4 based on the measured ph, another checker could tell you something a little different.
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