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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.

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35 Posts
Discussion Starter · #3 ·
Do you you have driftwood in the tank? Peat? What kind of substrate?
I have Flourite substrate, no peat, an two pieces of driftwood.
My pH used to be very low, like off the test kit low, between 6.4 and 6.0.
I added coral to see if i couldn't buffer the water.
Are you sure about your test kit readings?
I'm sure I'm reading them correctly. pH6.8 and 3degrees kh(3 drops of solution to turn from blue to pale yellow). These are AP test kits.
The simple fact is if you are not injecting CO2 you don't have more than about 3 ppm.
So Flourish Excel won't show up as CO2 ppm on this chart?

Thanks for clarifying.


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35 Posts
Discussion Starter · #5 ·
Since I have upped my light to 3.5 wpg and added more plants to my tank my parameters have been
0ppm N03
0ppm NH3
0ppm N02
I understand that I need to start to fertilize because my plants currently look like they are starving for Nitrates.
I ordered some from Greg Watson (sorry Rex I didn't realize at the time that you were also selling ferts).
Driftwood can and does leach chemicals into the water column that lower the pH.
Bastard! I was driving myself crazy trying to figure out why it was sinking like a rock - aside from being soft.
So is there a way to get driftwood that will not affect pH? Is it a problem with all types of driftwood?


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35 Posts
Discussion Starter · #7 ·
The AP instructions provide a table that shows:
|#of drops | deg KH | ppm kh |
|___ 3____|___3___|__53.7__|

So I think I'm reading that part right.

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35 Posts
Discussion Starter · #9 ·
What are your source water parameters?
Sorry I didn't register what you meant by source water.
Out of the tap it looks like this:
pH 7
kh 1 degree
NO2 0ppm
NO3 0ppm
NH3 0ppm
So the pH is going down and the kh is going up. Does that make sense?

I believe that the pH of the tap water drops a little after sitting around for 24 hours but I can't give you a number without testing it.

New question: In Rex's guide on water chemistry he says adding Baking Soda will increase the kh. I am now assuming that this increase has no effect on the amount of CO2 in the system. Is that right?
If so I'm starting to think that there are so many CO2 independent factors working on kh and pH that the CO2/kh/pH table is sort of useless. Is that right?


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35 Posts
Discussion Starter · #11 ·
OK so even if I pull the driftwood out and the ph rises from say 6.8 to 7.2.
The kh stays the same it only confirms what we already know... I low levels of CO2 in the tank.

So did I get a piece of booty driftwood? Or does all driftwood found in pet stores have this effect? Can I take it out and boil if for a couple of days to fix this leaching problem?

Those are the last questionsfor this thread, I promise.


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35 Posts
Discussion Starter · #13 ·
OK I lied about the last question thing.

So with driftwood in the tank it is pointless to use pH and kh to calculate the amount of CO2 as the pH reading is inaccurate. Yes?

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