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hoppycalif · 05-24-2006, 08:25 AM

I added a tiny amount of sodium bicarbonate to the sample so there would be ions in it. It takes a ridiculously tiny amount to reach a 4.5 KH. My probe is supposed to be accurate to 0.01, but I am quite sure it isn't, so I usually round off the numbers to the nearest .1, but didn't in this case.

What troubles me the most about this is that the distilled water with bicarbonate in it only climbed to about 1.0 in ppm of CO2 and did that relatively quickly. That suggests that our 24 hour outgassed tank samples have about 1 ppm CO2 in them and not 3, which means the 1.0 drop in pH is only 10 ppm of CO2 in the tank. Another test for another day would be to repeat that one, but first run some CO2 bubbles in it to raise the CO2 to well above 3 ppm, then see how low it drops in 24 hours. We have to use RO or distilled water for this to avoid having other sources of alkalinity in the water, making the KH/pH/CO2 relationship accurate.

In any case, at this point I don't think we know how much CO2 is in our tanks. So, increasing it to where the fish start to have problems, then backing off a bit is probably the only reasonably accurate method we have. I hope I am wrong about this.

05-24-2006, 08:25 AM	#4 (permalink)
hoppycalif Senior Member Join Date: Apr 2005 Location: Sacramento, CA, USA Posts: 5,208 iTrader Ratings: 20 iTrader Positive Rating: 100% Plant Points: 227345	I added a tiny amount of sodium bicarbonate to the sample so there would be ions in it. It takes a ridiculously tiny amount to reach a 4.5 KH. My probe is supposed to be accurate to 0.01, but I am quite sure it isn't, so I usually round off the numbers to the nearest .1, but didn't in this case. What troubles me the most about this is that the distilled water with bicarbonate in it only climbed to about 1.0 in ppm of CO2 and did that relatively quickly. That suggests that our 24 hour outgassed tank samples have about 1 ppm CO2 in them and not 3, which means the 1.0 drop in pH is only 10 ppm of CO2 in the tank. Another test for another day would be to repeat that one, but first run some CO2 bubbles in it to raise the CO2 to well above 3 ppm, then see how low it drops in 24 hours. We have to use RO or distilled water for this to avoid having other sources of alkalinity in the water, making the KH/pH/CO2 relationship accurate. In any case, at this point I don't think we know how much CO2 is in our tanks. So, increasing it to where the fish start to have problems, then backing off a bit is probably the only reasonably accurate method we have. I hope I am wrong about this.