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Old 09/22/2017, 02:03 AM   #1
gprdypoo04
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Unexpected alk jump

My alk just increased by 1.0 dkh over five days or so. I've been carbon dosing for awhile now because of my high nitrates. Would this cause my alk to increase if the bacteria is consuming my nitrates? Nothing has changed in the amount I dose for alkalinity. Went from 8.8 to 9.8 dkh . Usually the alk drops a little or is fairly steady.



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Old 09/22/2017, 10:31 AM   #2
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Maybe the demand changed? If it occurred over 5 days, I'd suspect it is caused by your dosing... That's not a drastic or dangerous change, so maybe just monitor it daily or every other day for now and see what it does. It if continues to raise, just adjust your dosage accordingly.


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Old 09/22/2017, 02:23 PM   #3
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Carbon dosing shouldn't raise the alkalinity level. I agree that a change in consumption is more likely. What is being dosed into the tank?


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Old 09/22/2017, 02:25 PM   #4
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Well... couldn't aggressive C dosing reduce nutrients too far & compromise growth (starve)... that would slow down consumption

Right?


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Old 09/22/2017, 03:14 PM   #5
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Yes, that would explain a change in consumption.


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Old 09/22/2017, 09:41 PM   #6
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Carbon dosing shouldn't raise the alkalinity level. I agree that a change in consumption is more likely. What is being dosed into the tank?

I dose 2 tablespoons of kalkwasser mixed with 20-25 mls of vinegar along with baking soda (baked) for alkalinity. Also recently started Pro bio S, NP Pro and the occasional Pro bio F. Also run bio pellets.


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Old 09/22/2017, 09:51 PM   #7
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I just checked my nitrates and still up around 30 to 40 ppm. It's strange my consumption would change though. Just have to keep an eye on it. Usually my alkalinity lowers a bit rather than increase unless I know I dose a little more. Oh well.....


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Old 09/23/2017, 12:05 PM   #8
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Carbon dosing doesnt have an impact on alk, however ive noticed I have to run lower alk while carbon dosing as sps can easily get burnt tips.


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Old 09/23/2017, 01:17 PM   #9
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I'm not getting any burnt tips.


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Old 09/24/2017, 12:05 AM   #10
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The Kalk will add alkalinity and calcium in the ratio that corals consume them, so adding more alkalinity (baking soda) is likely to spike the level over time.


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Old 09/24/2017, 12:50 AM   #11
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Really? Never considered that possibility.


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Old 09/24/2017, 02:25 AM   #12
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The Kalk will add alkalinity and calcium in the ratio that corals consume them, so adding more alkalinity (baking soda) is likely to spike the level over time.
When u say the above then why is it that I am still adding calcium chloride occasionally to keep up to the demand. The kalk that I dose only totals 8.4 mls in my 40 gal tank. That's why I also dose
a little baking soda as well to maintain my levels. Supposedly since my consumption has changed would it be better to dose only kalk?


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Old 09/24/2017, 11:16 PM   #13
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I would stop dosing the baking soda for a while, to see how that goes. Most tanks will be fine with Kalk only, although a few might need a bit more alkalinity. There are a few processes that will throw the ratios off:

http://reefkeeping.com/issues/2004-12/rhf/index.htm


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Old 09/25/2017, 12:51 AM   #14
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Thank u. I cut back on the baking soda but not entirely.
Will monitor it.


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Old 09/25/2017, 09:01 AM   #15
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Quote:
Originally Posted by gprdypoo04 View Post
I dose 2 tablespoons of kalkwasser mixed with 20-25 mls of vinegar along with baking soda (baked) for alkalinity. Also recently started Pro bio S, NP Pro and the occasional Pro bio F. Also run bio pellets.
The level of carbon dioxide in the tank will vary how much alkalinity you get from your kalkwasser mix I believe. When I run my skimmer air line outside, my tank ph goes to 8.2 from 7.8 if not running the air line outside. I need to use much less kalk when the ph is low, I'm guessing because the kalk reacts with the co2 more


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Old 09/25/2017, 03:08 PM   #16
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Kalk reacts with carbon dioxide to convert OH- into carbonate and eventually bicarbonate. The total alkalinity remains the same, but the pH of the tank will drop with the conversion, thus countering the initial spike due to the Kalkwasser. Air with more carbon dioxide should tend to push the conversion more rapidly.


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Old 09/25/2017, 03:15 PM   #17
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The pH doesn't drop due to the reaction, right?

The CO2 reduces the pH. But once the CO2 reacts with the OH- to make bicarbonate, the total Alk and pH are unchanged.

I think it's semantics but just to be clear.


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Old 09/25/2017, 05:58 PM   #18
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Well, technically, I probably am assuming that the tank continues to get more carbon dioxide from the air around the tank. I'd have to know more chemistry and work through pKa values to see how the pH responds in a system with no carbon dioxide available to enter the water column.


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Old 09/25/2017, 07:15 PM   #19
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But aren't the carbonate and bicarbonate speciations of the CO2 at that pH? Wouldn't they be at equilibrium already ?


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Old 09/25/2017, 08:14 PM   #20
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It's very likely that the tank will be close to equilibrium with the air, although photosynthesis can drive the pH up, thus causing a continuing influx of carbon dioxide. The tank is not at equilibrium with the air at that point, although the difference tends to be quite small, well, for my definition of "small". During the night, the pH can drop as photosynthesis stops, but at that point, respiration will drive the pH down at least a bit, leading to outgassing of carbon dioxide. I suspect that most systems only see a small effect, but I don't have any measurements. At some point, you'd need to define very carefully what you mean by "in equilibrium with the air", but in my view, as long as there's net carbon dioxide flux through the water surface, the system is not at equilibrium in that respect.

When the limewater is added, the calcium hydroxide will convert to calcium and carbonate ions, but I don't know how long that process takes. It might be fast enough that we can't easily detect any effect. I'll try to think about this a bit.

As a side note, if the lime is in the form of CaO, the first step is combining with water to form Ca(OH)2.


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