API KH test kit - Anyone with experience? Measuring CO2 Amounts - Page 3 - Equipment - Aquatic Plant Central

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Old 01-07-2012, 10:01 PM   #21 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

The ph/kH chart for co2 levels isn't another story at all, it's simply horribly in accurate and is useless for determining levels unless you can 100% say that there are no foreign entities in your tank water that could effect the ph.

I use a drop checker for the simplest indication and don't use it as a measuring device per se but rather to just know that co2 is being dissolved into the tank water. I actually don't try to measure the co2 levels and have no plans to. I just use my plants as an indicator for the co2. If you know what your looking at/what to look for they are all you need.
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Old 01-07-2012, 10:35 PM   #22 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

I find that one accurate way to measure CO2 is to do the test on two water samples: One sample freshly drawn from the aquarium and another sample from the aquarium that has been standing in a shallow dish, open to the atmosphere for 24 hours. In the second sample most of the CO2 will have diffused out and the CO2 content will be in equilibrium with the atmosphere which has 0.03% CO2. The difference between the two samples represents the meaningful CO2 content as far as your plants are concerned.
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Old 01-08-2012, 02:13 AM   #23 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

The KH tests are a type of test known as titration. This type of test relies on precise volume concentrations in the indicator and a volume of test material sufficient that the additions can be counted as insignificant. In hard water the API tests can be somewhat relied upon using their 5mL standard, but when the KH is low the difference from one drop to the next can be a significant difference. The only way to adjust for this is to use a larger volume of tank water and a control standard to calibrate the kit with. The best way to make a control would be to add baking soda to water using weighed amounts until it is saturated, then filtering off the undissolved portion and drying it, weighing the dried baking soda and calculating the CO3 content remaining in solution in ppm then testing how many drops it takes to change to determine the approximate ppm for each drop. Obviously this is more work than its worth if you have water with <5dKH. The pH drop method as described by HeyPK is a much more reliable and simple method than trying to accurately identify your KH and using pH/KH charts(not to mention the inherent unreliability in those charts if your water is buffered by anything other than CO3.)
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Old 01-08-2012, 08:26 AM   #24 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

I use a LaMotte test kit that titrates with a sodium hydroxide solution and phenolphthalein as the pH indicator. The titration is over when the solution turns pink. The difference between water in equilibrium with the atmosphere and water just out of the tank has got to be due to CO2 because there isn't likely to be any other substance that escapes into the air that affects the pH.

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Old 01-08-2012, 08:35 PM   #25 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

Im interested in what you had to say about judging your co2 by your plants Bsmith

"I just use my plants as an indicator for the co2. If you know what your looking at/what to look for they are all you need."

what exactly are you looking at and for?

im just curious cause i want to learn as well.
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Old 01-09-2012, 08:21 AM   #26 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

HeyPk, JUST to clarify: you test each sample for ONLY ph and measure the difference between the 2 samples, is that correct? (makes perfect sense, I'm just trying to make sure I wouldn't also need to compare the 2 samples for KH or GH or anything else as well...(I can't imagine WHY I'd need to, as I can't imagine either would change) )

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I find that one accurate way to measure CO2 is to do the test on two water samples: One sample freshly drawn from the aquarium and another sample from the aquarium that has been standing in a shallow dish, open to the atmosphere for 24 hours. In the second sample most of the CO2 will have diffused out and the CO2 content will be in equilibrium with the atmosphere which has 0.03% CO2. The difference between the two samples represents the meaningful CO2 content as far as your plants are concerned.
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Old 01-09-2012, 09:35 PM   #27 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

With my CO2 kit you titrate a sample of aquarium water with a NaOH solution until the indicator turns pink. You convert the # of drops into ppm CO2 using a chart. If you do 2 samples, one straight out of the tank and the other from the tank but allowed to stand for a day, and subtract, you get a more meaningful CO2 value. The CO2 that remains in water in equilibrium with the atmosphere isn't very much and isn't very available except for those plants highly adapted to being submerged and able to get CO2 from the bicarbonate ion, HCO3-, like Najas, Elodea, Ceratophyllum, etc.
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Old 01-10-2012, 12:17 AM   #28 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

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With my CO2 kit you titrate a sample of aquarium water with a NaOH solution until the indicator turns pink. You convert the # of drops into ppm CO2 using a chart. If you do 2 samples, one straight out of the tank and the other from the tank but allowed to stand for a day, and subtract, you get a more meaningful CO2 value. The CO2 that remains in water in equilibrium with the atmosphere isn't very much and isn't very available except for those plants highly adapted to being submerged and able to get CO2 from the bicarbonate ion, HCO3-, like Najas, Elodea, Ceratophyllum, etc.
That sounds terribly inaccurate. All you're doing is an acid/base titration so if there are any other things in the water acidifying it they will skew your results upward. Which is highly likely considering a lot of the biological processes involved in an aquarium will acidify your water by producing fulvic and humic acid, and then theres tannins if you have any driftwood. Measuring the pH difference is all you need. Which is pretty much what your describing in a roundabout way.

To the Big_Fish, atmospheric CO2 generally dissolves at 2.5-3ppm(pretty much exactly 1/100 of what is present in your ambient air and using 30ppm as 1 degree is a reasonable assumption). CO2 affects pH and if you isolate what is changing the pH to CO2 you get a measurement of CO2 as a factor of multiplication. CO2 is likely the only gas that changes pH in an aquarium, so by allowing the aquarium water to reach ambient levels of CO2 you will likely isolate CO2 as the culprit in any pH changes. pH is a logarithmic scale, meaning 1 degree=10 times the previous degree. So if you have a 1 degree drop you have 10 times what is present under ambient situations, and if you have less than 1 degree you can use the decimal as a multiplier against the total to get a rough idea of where your co2 is(e.g. if you have a .5 degree change you halve 30ppm to determine you have around 15ppm CO2.)
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Old 01-10-2012, 12:35 AM   #29 (permalink)
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Default Re: API KH test kit - Anyone with experience? Measuring CO2 Amounts

Quote:
That sounds terribly inaccurate. All you're doing is an acid/base titration so if there are any other things in the water acidifying it they will skew your results upward. Which is highly likely considering a lot of the biological processes involved in an aquarium will acidify your water by producing fulvic and humic acid, and then theres tannins if you have any driftwood. Measuring the pH difference is all you need. Which is pretty much what your describing in a roundabout way.
If all I did was the titration on the freshly drawn water from the aquarium, the other things acidifying the water could skew the results. By getting the difference between the two samples, I measure the CO2 lost when the one sample equilibrates with the atmosphere. Of all the things acidifying the water, only CO2 is volatile. The CO2 concentrations above the level of CO2 you get when your water is in equilibrium with the atmosphere are the CO2 concentrations of interest to aquatic plant growers.
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Old 01-10-2012, 05:08 AM   #30 (permalink)
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my brain hurts... why wouldn't you just gas the heck out of your tank until the fishies begin to surface for O2. then dail down until plants and fish are both happy?

i bet you a bush of staurogyne sp. purple CO2 levels are 30-35 ppm


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