Where did my carbonate hardness go? - The Planted Tank Forum
 
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post #1 of 3 (permalink) Old 06-24-2009, 05:51 AM Thread Starter
Ich
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Where did my carbonate hardness go?

And why doesn't my ph crash? I just tested my water parameters for the first time in a long time, and I was surprised to see my carbonate hardness (kh) was less than 10 ppm. Out of the tap it's about 30-40 ppm. My last water change was three and a half weeks ago. The other thing I don't get is that my Ph is 6.9, even though I have a fully stocked tank and basically no buffering capacity whatsoever. In fact, my kh levels have always been in the 30 ppm range, and the Ph never dips below 6.8 or so.

Here is some info about my tank:
- 32 gallon low tech with 40 watts of light
- home to about 20 pencilfish, five sailfin tetras, three farlowellas and a keyhole cichlid
- very, very heavily planted with crypts (it's a jungle - I can barely see the fish)
- no CO2, no water column fertilization, no peat, no carbon: some substrate fertilization with jobes sticks and seachem's root tabs
- water change of maybe 40% every three to four weeks
- hagen test kit that is admittedly a few months past its "best by" date

This may all be a test kit malfunction, but over the years I've been keeping this tank the kh has always been low, and the ph never, ever crashes. Every source I read says I'm supposed to increase the carbonate hardness to guard against ph crashes, but I've never done so, and the ph always stays steady at just below 7.0.

As for the drop in kh, and assuming the test kit is right, could the kh have been taken up by filter bacteria? By plants? I've never gotten a reading that low before, but I did increase the bioload higher than it has ever been by adding sailfin tetras. My working theory is that the increased bioload caused an increase in filter bacteria, which took up the carbonate hardness and caused a decline in kh, but that still doesn't explain the relatively high ph levels.

Fish and plants are happy, so this is a question out of pure curiosity. Does anyone have any thoughts about what might be going on here?
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post #2 of 3 (permalink) Old 06-24-2009, 04:31 PM
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With a known KH value of 3-5dkh my pH remains stable in the low tech tanks at a low of 6.8 and high 7.5pH.
2dKH usually tests as 6.8-7pH
3dKH = 7.2-7.4pH
4dKH I get a ph of 7.5 or real close to these numbers.

Depending on how much your bio load is producing respiration from organic decomposition, bacteria and fish contain CO2 and can lower KH somewhat. I have a new soil sub tank containing a lot of organic material and natural CO2 levels have been as high as 19ppm. Carbolic acid can reduce KH values in the water column. Iím probably not communicating this in perfect context but this may be whatís occurring in your tank.


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If at first you don't succeed,,, keep kicking it
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2-75g planted, 3-55g planted, 110g w/30g sump, 2018 update returning to sanity (Nutz)
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post #3 of 3 (permalink) Old 06-24-2009, 05:44 PM
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Some plants, especially vals, can use carbonates as a carbon source. They end up softening the water when they do this.


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