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post #1 of 20 (permalink) Old 11-08-2014, 10:23 PM Thread Starter
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alkalinity

My water is at .5 dkh. pressurized co2 high light tank.
Should I be worried about increasing my alkalinity?
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post #2 of 20 (permalink) Old 11-09-2014, 05:42 AM
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Hi Ssteve

At that low a DKH you basically have an unstable PH tank. It needs to be raised.

What is your gassed out exchange/replacements waters readings for PH, GH, and KH? Might as well post Ammonia, Nitrite and Nitrate.
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post #3 of 20 (permalink) Old 11-09-2014, 06:55 AM
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It's fine, don't worry about low kH.
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post #4 of 20 (permalink) Old 11-10-2014, 06:17 AM
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With the greatest respect I have to disagree with Solcielo lawrencia's last comment. Even if the tank has only plants, with an almost non-existent KH, the CO2 injection will completely destroy/use up the KH, and the PH could end up anywhere from 7 down to 4. Surely a stable PH is important for plant husbandry, as well as fish, is it not?

The easy fix is water changes with a decent KH.

If I have it wrong, please explain so I may learn more.

Thanks.
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post #5 of 20 (permalink) Old 11-10-2014, 06:25 AM
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Smile The Water Column is Inherently Unstable @ 0.5-dKH

Hi,

With all due respect I also disagree with Solcielo lawrencia, unless the particular breed of fish or plant you are keeping absolutely requires low KH, I recommend adding baking soda to bring the bicarbonate/carbonate hardness to 4-dKH.

Though I need to say to WaterKeeper that it is not CO2 injection that will “use up” the Alkalinity.

Respectfully,
Joe
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Last edited by JoeRoun; 11-10-2014 at 06:28 AM. Reason: Left a bit out
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post #6 of 20 (permalink) Old 11-10-2014, 08:14 AM
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Well this is interesting.

I thank JoeRoun for agreeing with me re the almost non-existent KH and the possible disastrous PH outcomes.

That said though, I unfortunately can't agree with JoeRoun (with the greatest respect) re CO2 not affecting KH. CO2 is a basic acid, and attacks/consumes bi-carbonates (in fresh water).

I suppose it comes down to how much CO2 the plants can consume while lights are on. What happens when lights are off?

It seems I'm disagreeing with 1 member, and agreeing with another member who supported me on one (the first) point, and disagreeing with that supporting member on the second point?!

I hope I haven't upset the apple cart here.
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post #7 of 20 (permalink) Old 11-10-2014, 03:51 PM
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Hi WaterKeeper,

If the CO2 alters KH is a matter of religious belief, if a Rabbi, Priest, Guru, Muftis, Preacher, Minister, Clergy person, religious leader tells you differently and you are a true believer accept what they say, I will not argue.

If it is not dogma to you than the simple fact is that CO2, or the small bit (~1/400) that becomes carbonic acid simply does not consume bicarbonate/carbonate hardness (KH).

However, the simple explanation of CO2/KH relationship is that the consumption of KH by any acid is actually the release of (phase change to gas) CO2 from bicarbonate/carbonate, carbonic acid (the names kind of give it away) take a carbon, leave a carbon, no net change. (Kind of stole that line from mattinmd.)

Without getting into the dual pKa thing, it should stop and make folks think that when we add 30-ppm CO2 (solvated) to our tanks we only produce about 75-parts-per-billion (ppb) carbonic acid yet can see a full unit drop in pH.

Anyway you are in good company.

Respectfully,
Joe
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Last edited by JoeRoun; 11-10-2014 at 03:54 PM. Reason: (Kind of stole that line from mattinmd.)
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post #8 of 20 (permalink) Old 11-10-2014, 06:23 PM
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I generally agree that low KH is pretty undesirable, but I would make one possible exception to the need to raise KH...

If your water is phosphate buffered, the low KH isn't a big deal as you've got plenty of buffer that isn't being measured by KH. Call your local utility to find out of they do that (not terribly common, but some places do treat the water this way..).
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post #9 of 20 (permalink) Old 11-10-2014, 10:10 PM
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Joe

However, the simple explanation of CO2/KH relationship is that the consumption of KH by any acid is actually the release of (phase change to gas) CO2 from bicarbonate/carbonate, carbonic acid (the names kind of give it away) take a carbon, leave a carbon, no net change. (Kind of stole that line from mattinmd.)


is the takeaway from that accurately restated if we say hydrochloric acid actually does consume the kh because its not leaving a carbon behind as it acts on kh constituents


the one factor Ive been wanting to distill from these posts is why the acid action, h+ donation, from carbonic acid acts differently on kh vs any other ole acid.

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post #10 of 20 (permalink) Old 11-11-2014, 12:42 AM
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If you react hydrochloric acid with carbonate, the reaction is as such:

2 x HCL + CO3 = H2O + CO2 + 2 CL-

So you've neutralized a carbonate, creating water, carbon dioxide and a couple chloride ions left behind.

If you react carbonic acid with carbonate

H2CO3 + CO3 = CO3 + H2O + CO2

See, when you strip the H2 part off the carbonic acid, and use those H+ ions to neutralize one carbonate, it leaves behind another carbonate that was part of the carbonic acid. Net carbonate change - zero.

This is why carbonic acid can't reduce KH.. It is a carbonate on its own and every carbonate it reacts with will result in a different carbonate being left behind.
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post #11 of 20 (permalink) Old 11-11-2014, 01:53 AM
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I have several tanks with very low KH, and they are stable.
The montmorillonite clays will remove the carbonates from the water.
The water company adds sodium hydroxide to the water to keep the pH up.
Perhaps the substrate removes this, too, because the pH stays very low in these tanks. Took a lab test to find out the pH was 5.8.

When I add carbonates (bicarbonate of soda or potassium bicarbonate) I can raise the KH, but it drops as the substrate removes the carbonates. I can add oyster shell grit or coral sand to the filter and this will help a bit, and is more stable.

When I want to set up a hard water tank I use coral sand. This is great for Rift Lake fish, many live bearers, brackish water tanks...

Anyway, back to the original question, which I will answer with a question:
What is the GH? Is this what the fish want?
If so, I would make the KH pretty close to the GH, and this ought to help the pH be in the right range for the fish.
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post #12 of 20 (permalink) Old 11-11-2014, 02:58 AM
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The buffer for pH is the combination of carbonic acid from the CO2 in the water and the carbonates (KH) in the water. The pH that this buffer maintains depends on how much KH and how much CO2 is in the water. Those two determine the pH of the tank water. But, a buffer is only effective against small additions of acid or base, so our tanks are never immune from a pH change due to addition of an acid or base to the water. Fortunately, we don't, or at least we shouldn't add an acid or base to the water. The acid from peat or other organic matter is a very weak one, so that doesn't do a lot of harm.

(This is my current interpretation of the effect of KH and CO2 on tank water, so it may be off a bit, if not a lot.) For sure, KH is not a buffer, so more KH does not mean more buffering. In fact more KH causes the pH to go up, not be more stable.

So, to answer the question: low KH is not bad. With pure distilled water, with no substrate, you could have zero KH, and that would be bad. Normal aquarium water always has a KH above zero.

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post #13 of 20 (permalink) Old 11-11-2014, 04:33 AM
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Hi Brandon, WaterKeeper, All,

Mattinmd’s answer is the straightforward answer I endorse, in fact would have given. There are reasoning that is more complex, but they all require a little more chemistry.

As I said earlier if you are a true believer and your Rabbi, Priest, Guru, Muftis, Preacher, Minister, Clergy person, religious leader says different accept what they say, I will not argue.

Respectfully,
Joe
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post #14 of 20 (permalink) Old 11-11-2014, 01:56 PM
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After years reading about this on reefcentral chem board and elsewhere I vote this as the most concise and I get it yay

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post #15 of 20 (permalink) Old 11-11-2014, 05:50 PM
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Chemistry is chemistry, what someone believes is interesting but can't really change reactions...unless you concentrate really hard!

Pragmatically, KH doesn't matter unless low KH has shown to have caused a pH crash in a particular tank maybe because of infrequent pwc's or high stocking. The general advice of setting KH at 3-4 min probably isn't bad for the average hobbyist who doesn't fiddle with their tanks a lot.

The salient point about buffers is that more useful buffers are weak bases/acids and their conjugates, they have strong bonds and don't react completely and quickly.

A great site I found that very clearly describes buffers in a simple manner is:
http://www.monashscientific.com.au/p...Solution.htm#7

Following the articles' links goes into titration curves and all the geeky stuff.

Not sure why an Australian glass blowing for wine makers company would post all these excellent tutorials, but they did a nice job.

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