.5 pH drop 8 ->7.5, is there enough CO2? - The Planted Tank Forum
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post #1 of 3 (permalink) Old 02-05-2019, 07:36 PM Thread Starter
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.5 pH drop 8 ->7.5, is there enough CO2?

According to the chart, if the KH =4 and pH drops from 8.2 to 7.6, there is still virtually no CO2 in the water.

Is this correct? I am setting up a passive CO2 diffuser and it only lowers the water about 1/2 of a point. OTH, that CO2 is going somewhere and its not an insignificant amount.

However, in my main tank with CO2/griggs, the pH drops from 8.2 to 7.0, yet with KH =4, the table says I only have 12ppm, and there is mad pearling. Is that correct?

Conventional wisdom is to drop pH by one whole point, yet my tap water which is high pH, low KH... would need to drop much more for 30ppm.

What is going on with this water?

If I ran it through a RODI unit, it would come out at pH 7, HK 0. If I reconsititute it to KH 4, the pH would be around 7.2, and even without injection, the water would be said to have around 10ppm CO2 according to chart. Which is much more than same water has (sans RODI) with passive diffuser CO2 injection *according to chart*.

According *to the chart*, using an RODI on my water and reconsituting with Alkaline Buffer, would have a more beneficial effect on CO2 than actual CO2 injection.

There is obviously some kind of buffer in the tap water, does that actually inhibit CO2, or just fake out the pH test/CO2 relationship?


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Last edited by ChrisX; 02-05-2019 at 07:56 PM. Reason: asdf
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post #2 of 3 (permalink) Old 02-05-2019, 07:40 PM
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Throw that chart out the window, it is not accurate in my (and many other's) opinion.

If you're dropping pH and injecting CO2 with a kH of 4, than CO2 is certainly being dissolved producing the pH drop.
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post #3 of 3 (permalink) Old 02-05-2019, 10:18 PM
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Quote:
Originally Posted by ChrisX View Post
What is going on with this water?
Yeah Chris those are some strange numbers.

Are you still using API liquid test? Or a calibrated probe?

Is that reading right from the tap? You ever let a sample sit out for several days to see if it changes?

What is the reading in the tank right before CO2 comes on??


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