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View Poll Results: Whats your KH in your planted tank??
0 2 4.88%
1 4 9.76%
2 4 9.76%
3 8 19.51%
4 6 14.63%
5 or Higher 18 43.90%
Multiple Choice Poll. Voters: 41. You may not vote on this poll

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Old 04-18-2012, 12:01 AM   #1
happi
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Default KH and plants

i understand that you cannot messure the co2 levels when you have 0 KH, but does this have any effect on co2, i was reading somewhere Tom said that CO2 doesnt disslove very well under 0 KH. i always thought the lower the KH the better it is for plants. i just want to hear your opnions on this, i been keeping fish and plants under these condtions for long time now. i never really seen any fish stressed under these condtions, my plants are ok too, but not the best. i just want to see if anyone is sucessfully keeping plants under 0 KH
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Old 04-18-2012, 12:14 AM   #2
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I don't believe that anyone really has 0 KH because the pH of water with 0 KH would be about 4.3. I suspect that your KH is below the test limit of the test you are using. Anyway, I have no experience using such low KH water. I mix my RO with tap to get 4 deg KH.
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Old 04-18-2012, 12:29 AM   #3
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Originally Posted by ray-the-pilot View Post
I don't believe that anyone really has 0 KH because the pH of water with 0 KH would be about 4.3. I suspect that your KH is below the test limit of the test you are using. Anyway, I have no experience using such low KH water. I mix my RO with tap to get 4 deg KH.
now the real question is what if the KH was 0, how will the effect the co2 and plants. i know my test kit cannot messure lower than 6.0 PH, but API test kit for KH always change color with 1 drop. am sure KH levels are almost 0, because am using 100% RO.
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Old 04-18-2012, 01:54 AM   #4
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It'll be interesting how the titration of an API alkanity kit actually works i.e. what is the chemistry theory? but a might be a patented chemistry process...

someone has a link?

Most calcium exists as a carbonate, but high hardness/low alkanity is indicative of a magnesium sulfate, phosphate or other non-carbon calcium compound?
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Old 04-18-2012, 01:57 AM   #5
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Try doubling the sample water used in the test kit. Instead of 5 ml, use 10 or even 15 then count the drops to get a more accurate measurement of your kh.
Also, I think even if using RO water, there will be some kind of buffer due to aquasoil or tannins etc.

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Old 04-18-2012, 03:10 AM   #6
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My kH is 0 according to the test kits. Ofcourse its more like less than 1 but higher than 0. I dose ferts after all.

My pH is wicked low though. Like 5.1 sometimes 4.5 in my co2 injected tanks. Having said that, I never really had a problem with kH for plants. It was always more about not having enough of some nutrients for me.
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Old 04-18-2012, 03:50 AM   #7
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I don't see how KH can ever be below zero. Intuitively I think the KH could only approach zero asymptotically, never quite reaching zero.
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Old 04-18-2012, 03:55 AM   #8
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I don't see how KH can ever be below zero. Intuitively I think the KH could only approach zero asymptotically, never quite reaching zero.
then why people are adding baking soda etc????
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Old 03-09-2013, 03:44 AM   #9
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Originally Posted by happi View Post
then why people are adding baking soda etc????
I'm not sure, the old dogma was to prevent pH crash, but that seems to be a myth. In fact, I'll say it; it is a myth.

Like yourself, I've found little support for it. I've also never heard of issues that we could verify that it was due to the KH alone and not just the old general CO2 problem people have regardless of the their KH.

Maybe a dozen or so folks have had 0 KH range water or used RO/DI post systems. KH is not absolute zero, but conductivity readings in the 3-15 uS ranges is pretty pure water.

The form the CO2 is in, is CO2[aq] mostly when we add /enrich with CO2 gas....... regardless of KH. The ratio is roughly 1:400 for H2CO3:CO2. HCO3 plays soem role, but I'll eat ghost pepper if someone wants to try and claim they can soften the KH with CO2.

I think folks trip over this when they are thinking about equilibrium systems where they are not adding CO2 gas. This is likely the source of the mix up, that and misunderstanding about how much of the CO2 is in the form H2CO3(not much).

Since only 0.25% changes to H2CO3, there's virtually no measurable effect on KH when we add CO2. Any hobbyists can measure their KH before and after adding CO2 to prove this to themselves.

Did your KH change? Nope.

If you added a stronger acid, say acetic acid, then this will attack the KH and remove it(liberating CO2 in the process and reducing the KH), or HCL etc. CO2 is not going to do much at all, in reality a tiny bit does occur, then only a tiny bit.

Measuring pH is tough without any alkalinity however.

But if you add the same rate of CO2, say 500mls of gas per 60mins to a 20 gallon tank, whether that aquarium has a KH of 0,2, 5, the CO2 will be pretty close to the same in all cases.

You may use this approach with DI/RO water, peat , tannins etc, and then bump the KH up to get your measurements, then remove the KH with water changes etc.
I use to do that to try and measure CO2 when I use dpeat and have a lot of wood I suspected of depressing pH and altering KH measurement.
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Old 03-09-2013, 03:42 PM   #10
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Quote:
Originally Posted by plantbrain View Post
I think folks trip over this when they are thinking about equilibrium systems where they are not adding CO2 gas. This is likely the source of the mix up, that and misunderstanding about how much of the CO2 is in the form H2CO3(not much).

Since only 0.25% changes to H2CO3, there's virtually no measurable effect on KH when we add CO2. Any hobbyists can measure their KH before and after adding CO2 to prove this to themselves.

Did your KH change? Nope.
It is kind of interesting how little is known about KH!
KH has nothing, zero, nada to do with the amount of CO2 in a sample or even the amount of bicarbonate/carbonate in a sample.
1.4825 mmol/L of NaHCO3, NaOH, KOH, etc all are 4.00 deg KH
Also
0.71423 mmol/L of Na2CO3, CaCO3, Ca(OH)2 etc. are all 4.00 deg KH
It takes the same amount of HCl to titrate any of these to a pH of 4.5 so they all have the same KH.
Even something that is not in the carbonate buffer system like CaSO4 has a measureable KH but technically that would be considered total alkalinity.
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Old 04-18-2012, 03:57 AM   #11
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I don't see how KH can ever be below zero. Intuitively I think the KH could only approach zero asymptotically, never quite reaching zero.
No I don't mean less than 0. I mean 1< x >0. Less than 1 greater than 0 degrees of carbonate hardness. My test kit is accurate up to 1 degree. But I can't test in PPM which I suspect will give me a more accurate amount. Albeit a very low amount.
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Old 04-18-2012, 04:27 AM   #12
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No I don't mean less than 0. I mean 1< x >0. Less than 1 greater than 0 degrees of carbonate hardness. My test kit is accurate up to 1 degree. But I can't test in PPM which I suspect will give me a more accurate amount. Albeit a very low amount.
are you using 100% RO water??
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Old 04-18-2012, 12:08 PM   #13
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Quote:
My pH is wicked low though. Like 5.1 sometimes 4.5 in my co2 injected tanks
The pH of carbonic acid in normal atmospheric conditions is about 5.5. The pH of your tanks suggests that either pH test is off or you have stronger acids at work in your tank.
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Old 04-18-2012, 06:17 PM   #14
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The pH of carbonic acid in normal atmospheric conditions is about 5.5. The pH of your tanks suggests that either pH test is off or you have stronger acids at work in your tank.
I have ADA aquasoil. O kH and 0 gH.

Its right out of the tap. However, it must also be noted my water is slightly cooler than the average. Around 68-65 which means it can hold slightly more dissolved gasses than the normal room temeperture. So with that combined, I think it draws down my pH a little more.
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Old 04-18-2012, 01:49 PM   #15
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I never thought I would get a chemistry lesson at a fish forum lol. I never knew what the ph of carbonic acid was at normal atmospheric conditions......My kh is like 7 or 8 and I never had problems growing aquatic plants.....co2 was still effective, you would just need more of it. Also, aren't ph swings highly likely without any buffers? I never ever ever would use 100% RO/DI water. There are no buffers at all, nothing to keep the ph stable, that's why they sell buffers to add back to RO water to reconstitute it. I would at least keep the kh at 3 or 4 degrees. 0 kh sounds crazy to me.
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