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post #1 of 39 (permalink) Old 09-23-2014, 02:04 PM Thread Starter
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Water Chemistry

I was trying to lower the pH from 8.9 to 7.0 and to also reduce the very hard water from my tap to make it soft-to-medium hardness. I mixed RO water with my tap water (50-50) and then added dilute sulfuric acid a few days later (ph down solution). I thought that using ro water would reduce the hardness quite a bit and lower the pH a little too -- and that by then using the acid after I mixed my water it would leave some minerals as a buffer against wild pH swings. The first part work fine (cutting my tap water with ro water) but after adding the acid (a few days later) my Kh went to zero (because the sulfur has bonded with all of the bicarbonate and carbonate ions, right? I was expecting that, I think). But why did my Gh go UP! (and by the same amount the Kh went down?!). Does anyone know what's going on with my water chemistry? I though the gH would remain the same and that my TDS would decrease. It looks like my TDS has remained constant and the carbonate and bicorbonate ions have bonded with the sulfuric acid in such a way as to create Magnesium and Calcium ions. I can't remember my school chemistry but that doesn't seem right. I should be getting "salts" in the water, maybe like sodium sulfate but why would I get more Magnesium and Calcium ions? What am I missing?

Thanks in advance,
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post #2 of 39 (permalink) Old 09-23-2014, 04:24 PM Thread Starter
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Update.

Okay so the Kh is bouncing back. I didn't wait long enough for the reaction to complete. If it settles at pH 7.5 I'll stick with that. Am I right in saying that given that when aquariumists talk about a "buffer" they are essentially talking about the logarithmic nature of the pH scale -- so that the more alkaline a solution the more stable in it's alkalinity, or alternatively, the more acidic a solution the more stable it is in its acidity. It goes without saying then that it would not be possible to have a "buffer" with the water at pH 7.0, right? Otherwise it would not be neutral, right (it would have alkaline compounds in it (the carbonate or bicarbonate), right?)? Furthermore you could presumably add a "new buffer" after reducing the pH, without altering the newly created pH 7.0, which wouldn't make sense because adding carbonate or bicarbonate would just build back up the buffer you destroyed to lower the pH (and simultaneously increasing the pH), which would just take you back to where you started but with harder water and additional sulfur compounds.

Is Kh, in practice, more often than not, just a measure of the alkalinity of a solution?
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post #3 of 39 (permalink) Old 09-23-2014, 04:43 PM
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Originally Posted by david765 View Post
Am I right in saying that given that when aquariumists talk about a "buffer" they are essentially talking about the logarithmic nature of the pH scale.
You are incorrect. http://en.wikipedia.org/wiki/Buffer_solution
A buffer solution can be created for almost any pH.

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Is Kh, in practice, more often than not, just a measure of the alkalinity of a solution?
kH is by definition a measure of alkalinity. Alkalinity has a relationship with pH, but they are not the same thing.


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post #4 of 39 (permalink) Old 09-23-2014, 04:48 PM Thread Starter
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Thanks. So why don't people just destroy the Kh buffer, lower the pH with sulfuric acid, and then add a new buffer?

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A buffer solution can be created for almost any pH.
But presumably you couldn't have a Kh buffer for an acidic or neutral solution (otherwise it would be "used up" or contribute to an alkaline solution), yes?
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post #5 of 39 (permalink) Old 09-23-2014, 07:33 PM
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Hi,

If you are using the product ‘pH Down,’ you are using a 29% phosphoric acid solution and I agree with 691175002, you might as well make your own, targeting the specific pH you wish to keep.

Were you to be using sulfuric, hydrochloric or any other strong acid to lower KH (buffering) to lower the pH, you would need to strongly aerate, to blow-off (degas, the gentry would say) the C02 to keep the carbonates/bicarbonates (at our pH’s, nearly all bicarbonates), since the chemical reactions move in both directions.

Mixing the proper proportions of RO will work, though it may take a few water changes to establish the ‘equilibrium’ condition you desire.

Not to get too technical (controversial around here), since you are really measuring the acid-neutralizing capacity (ANC) of solutes plus particulates in an unfiltered water sample, once you have added phosphoric acid to the solution (aquarium water) the one thing we know for sure is that your measurement is no longer (assuming it once was) limited to carbonate hardness (KH).

My recommendation is that you experiment with various RO (reverse osmosis), tap water combinations until you get what you want. Using small containers (Mason jars for example) allows you to look at many combinations in a short period of time. This process can also help you figure out precisely what you need to do to get your aquarium water where you want it so everything else works as well.

Respectfully,
Joe
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post #6 of 39 (permalink) Old 09-23-2014, 08:41 PM Thread Starter
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Thanks for your answers guys.

Okay. It boils down to the fact that I want water that is pH 7-7.5 soft-medium hardness and with a reasonable buffer to protect from pH swings.

How do I do this? My attempt to go 50-50 with ro water and tap water, and then dropping the rest with acid, just isn't giving me enough of a buffer. How would I correct this? Can I correct this? I'm worried that my fish will hit a pH swing and die.

My water is very-very hard and the pH is 8.9. What would people recommend?
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post #7 of 39 (permalink) Old 09-23-2014, 08:56 PM Thread Starter
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Originally Posted by JoeRoun View Post
Were you to be using sulfuric, hydrochloric or any other strong acid to lower KH (buffering) to lower the pH, you would need to strongly aerate, to blow-off (degas, the gentry would say) the C02 to keep the carbonates/bicarbonates (at our pH’s, nearly all bicarbonates), since the chemical reactions move in both directions.
wtf? Are you serious? I need to blow my dilute sulfuric acid and it will help keep my Kh buffer? You're having me on, right? I though Degas was a painter? Are you serious mate?
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post #8 of 39 (permalink) Old 09-23-2014, 09:11 PM
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I would target gH first (via mixing RO and tap water), then kH (via baking soda), and leave the pH where it ends up.

Shifts in pH aren't nearly as serious as shifts in other parameters. Some causes of pH shifts, such as CO2, really don't seem to bother fish at all.

The tank itself will generally provide buffering capacity in several ways, including decaying organic matter, dissolved carbon, phosphate and more (driftwood/soil/peat are good contributors). If you control the gH and kH I suspect you will see a moderate pH once the tank settles in.

Trying to forcefully control pH is a tough battle since you will be continuously fighting the aforementioned processes.


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post #9 of 39 (permalink) Old 09-23-2014, 09:14 PM
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Hi,

No intention to offend, a thousand pardons… A little chemistry is all.

I am pretty sure you were not using sulfuric acid anyway…

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Joe
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post #10 of 39 (permalink) Old 09-23-2014, 09:50 PM Thread Starter
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1.) I was using sulfuric acid. In the UK the "pH down" is dilute sulfuric acid -- besides I bought a tub of sulfuric acid commercially -- it was too expensive to buy it from the pet shop. I then mix it with di-ioinised water to a strength of 8-10%. I can attach a photo if you really care.

http://www.amazon.com/API-Down-Aquarium-Adjuster-16-Ounce/dp/B0002ASGBS
(I think this was the stuff I originally bought...then looked at the ingredients and sourced them myself. Dilute sulfuric acid.)

2.) Why would I add baking soda (and when?)? You mean if i were to crash the pH down I would add it to re-buffer the water and increase the ph to the desired level? Yes?

I'm sorry if I'm stupid.

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post #11 of 39 (permalink) Old 09-23-2014, 10:20 PM Thread Starter
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I *AM* stupid!
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post #12 of 39 (permalink) Old 09-23-2014, 10:25 PM
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Hi,

If you added sulfuric acid, the net result without strong aeration would be zero, nada, nothing, equilibrium will return, whatever buffer they are using it is not sulfuric acid.



If Her Gracious Majesties government would allow such a thing it would only be to punish the impudent people that would dare think they could enjoy liberty and breathe the air as free men and women; to think to vote as to be free, such nonsense.

I, at no point, recommended adding baking soda.

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post #13 of 39 (permalink) Old 09-23-2014, 10:29 PM Thread Starter
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I can assure you it is sulfuric acid. Why would this not work? I am SO F-ing confused. Thanks in advance.
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post #14 of 39 (permalink) Old 09-23-2014, 11:22 PM
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Hi David,

Let us start over, let us stick to respectful conversation, even when we do not agree. I have some history with being angry and it does not foster good communications.



My apologies as well for the Scottish vote references, I am a resident of Jersey, the Channel Islands, so your Queen is my Duke (go figure) and of course Jersey is a Royal Peculiar, which is I, gather, the reason they let me in.

I suggest you read my Lowering KH via Lime & Muriatic Acid thread. That may explain part of it.

Avoiding getting technical, I need to ask you to accept that this is an “equilibrium reaction,” a fancy way of saying this reaction happens in both directions.

In your case this means that even though you added enough acid, to overcome the buffer. KH, carbonate/bicarbonate hardness, at normal freshwater fish (especially planted tanks) pH this is pretty much all going to be bicarbonate, is principally a buffer against pH changes.

Any acid (sulfuric or otherwise) you add will “use up” (actually it is changing some bonds) buffering capacity. When you add enough acid to overcome the buffering the pH drops until a new “equilibrium” is reached. If you leave it alone at this point and nothing is done to remove the bicarbonates, the process will begin to reverse and those bicarbonate bonds will reestablish.

Once you have added enough acid to “use up” enough of the bicarbonates, to make the pH permanent, aerate (vigorously) the solution (aquarium in this case) to drive off the CO2, so that the carbonates/bicarbonates cannot reform.

I will look into this API pH Down, somewhere somehow they are modifying the buffering arrangement. I do this all of the time with phosphates, which as it happens also provide plant food.

I suspect the API thing is to avoid using phosphates due to the (irrational?) fear many seem to have of phosphates.

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Joe
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post #15 of 39 (permalink) Old 09-23-2014, 11:53 PM Thread Starter
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Okay. Thank you for your time and patience.

1.) When you say the reaction is an “equilibrium reaction” you mean that elements can take an acidic or alkaline form depending on whether this a free H+ or -OH ion available to bond with x, y, z element. The "buffer" is really the depth of a bell-curve distribution of free ions, right?

2.) Considering I have an ro machine do I need to be mucking around with acid?
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