[Brendan Redler]

uhhh...last night I re-did my CO2 brew with a new mixture and it's going like crazy. According to my pH of 6.4 and my KH of 5.6, I have about 68ppm CO2. Am I going to kill my shrimp?

 

[Muirner]

68PPM is rather high, well about double and then some of what i'm running in my tank, i'd advise to get an airstone in or some sort of surface aggitation and lowering it a little. That's at least, my opinion

 

[hoppycalif]

If you use a drop checker per http://www.aquaticplantcentral.com/...aquarium-projects/32100-diy-drop-checker.html you will have a much more accurate idea about how much CO2 you have in the tank. Measuring the pH and KH of the tank water doesn't give you an accurate measurement of CO2, and it generally gives a high reading.

 

[Brendan Redler]

If you use a drop checker per http://www.aquaticplantcentral.com/...aquarium-projects/32100-diy-drop-checker.html you will have a much more accurate idea about how much CO2 you have in the tank. Measuring the pH and KH of the tank water doesn't give you an accurate measurement of CO2, and it generally gives a high reading.

I have a drop checker on the way from e-bay. I found an ADA one that I got for $26 brand new .

but seriously...even if the reading was 20-50% high, I would still be on the very high side of things. Hmmm perhaps that's why you are skeptical about the high reading? Anywho, the shrimp seem to be doing okay, except that I seem to be missing some of the smaller ones.

 

[bgzbgz]

A more accurate way to check co2 would be to take a cup of water from your tank and measure the ph of the water. Then wait 24 hours and test the ph again. For every .5 difference of ph thats 15 ppm of co2. So for example if your ph was 7.0 on the first test and 6.0 on the second test you had 30 ppm co2 in your tank.

 

[hoppycalif]

A more accurate way to check co2 would be to take a cup of water from your tank and measure the ph of the water. Then wait 24 hours and test the ph again. For every .5 difference of ph thats 15 ppm of co2. So for example if your ph was 7.0 on the first test and 6.0 on the second test you had 30 ppm co2 in your tank.

This doesn't work either! I found when I did some testing on this method that 24 hours isn't really long enough for the pH of the water sitting there to stop rising. Another guy doing the same testing found it took more than 2 days, as I recall. And, it still isn't at all clear what the ppm of CO2 will be in the water after it sits that long. It could be 0.4 ppm, or it could be 4.0 ppm. In the first case the 1.0 pH change means only 4 ppm of CO2 in the tank water, but in the second case it means 40 ppm. And, a .5 difference in pH would mean about 70% of the amount of CO2 that a difference of 1.0 means. About a .3 difference in pH is what means 50% of the amount of CO2. (It is proportional to 10 to the power of the pH difference. 10 to the .5 power is about 7, 10 to the .3 power is about 5.)

 

[ray-the-pilot]

Try this (modified USP method)
Take a sample of water. Check the pH. Boil the water for 5 min. Let it cool back to room temperature. Recheck pH.

If your water is very close to pure you may need to add a small amount of KCl but ordinary tank water is probably not a problem.

This will absolutely give you an estimate of the amount of dissolved CO2 in the water.

 

[hoppycalif]

When you boil water the water changes from liquid to gas, and the gas escapes. But, the bulk of the ions that were in the water remain in the water. So, less water is there after boiling, but the same ions are still there, so you then have a higher KH, GH, and you concentrate any acid or alkalinity causing ions, not counting the CO2, which escapes with the water vapor, but atmospheric CO2 immediately starts dissolving back into the water. How does this allow you to determine how much dissolved CO2 is in the sample? A good experiment would be to try this, starting with distilled water and a tiny bit of baking soda.

There may be a way to use the boiling idea, but I don't see it yet. More thought always helps!

 

[ray-the-pilot]

When you boil water only a miniscule amount of the water is vaporized. Say 1 gram out of 1000. Since pH is a Logarithmic scale that is a difference in pH of .001. I think you can live with the difference between a pH of 7.000 and 7.001 If you are really worried about that, start with a larger volume of water.

BTW The KH and GH go down when you boil water. This happens when you drive off CO2. The HCO3- concentration goes down and the CO3(-2) conconcentration goes up. CaCO3 and MgCO3 are much less soluble than their bicarbonates and precipitate out. This is the basis for temporary vs. permanent hard water and why your tea kettle fouls up.

If you go to this wiki site:
http://en.wikipedia.org/wiki/Hard_water
and read about temporary hard water it explains it better than I can