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Old 01-12-2015, 07:38 AM   #31
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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.

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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Old 01-12-2015, 09:14 AM   #32
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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-C.../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).
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Old 01-12-2015, 11:56 AM   #33
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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-C.../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).

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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Old 01-12-2015, 07:21 PM   #34
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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/2...arium.html?m=1
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Old 01-12-2015, 07:30 PM   #35
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CO2 chart

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.
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Old 01-12-2015, 09:30 PM   #36
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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.
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Old 01-13-2015, 03:06 AM   #37
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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.

What Is the premixed reference solution dkh?


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Old 01-13-2015, 05:43 AM   #38
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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 .
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Old 01-13-2015, 06:01 AM   #39
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If it's a premixed solution it's gonna be 4dkh.
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Old 01-13-2015, 06:45 AM   #40
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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 .

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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