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Claculating CO2

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I am trying to get an idea of my CO2 levels. I've done the initial pH & kh tests and am wondering if anything could be throwing them off.

I have a pH of 6.8 and a kh of 3 degrees. According to Chucks planted aquarium calculator I'm rocking 14 ppm CO2.

Which is weird because I am not putting in CO2 gas.
I am adding Flourish Excel every-other day. Can Excel really work that well?

Also I am not using any pH buffers or phosphates right now EXCEPT for about a pound of crushed coral in my substrate (20 gallon tank). I have been told by a pretty reliable LFS that Seattle doesn't have any phosphates out of the tap.

So is my reading accurate?
Does the coral affect my CO2 readings in a deceptive way? (I've read that dissolved CO2 or H2CO3 will dissolve some of the carbonate and increase kh. Which means that if the coral is affecting the kh it is because of the presence of CO2 and therefore shouldn't give a false sense of how much CO2 is present. Is that right?)

Finally I did use Seachems Neutral Regulator at one time a few months ago. As I understand it this is a phosphate that adjusts the pH to 7 and would definitely give me an inaccurate reading. How long would it take for this stuff to leave my system with 300gph filtering and weekly 50% water changes?

I hope all this info makes sense. I'm still trying to wrap my head around the chemistry.

thanks
pairustwo
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The crushed coral would have no effect on the pH/KH/CO2 relationship.

Do you you have driftwood in the tank? Peat? What kind of substrate?

Are you sure about your test kit readings?

The simple fact is if you are not injecting CO2 you don't have more than about 3 ppm.

Also if you have crushed coral in the water then your pH and KH should be higher than that.
 

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Oh... the light bulb comes on!

Baking soda will raise KH but also raises pH.

TANSTAAFL = There Ain't No Such Thing As A Free Lunch.

The pH of your source water will vary a bit as it doesn't have a lot of buffer. Try doubling the sample size on your KH test kit (10 ml of water instead of 5). That will make each drop equal 0.5° of KH.


KH is going up from the crushed coral and the pH is going down from the driftwood.
 
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