Lake Malawi Species • PH level

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PH level

Postby Funkster » Sun Aug 23, 2020 1:57 pm

My PH in my tank averages out at 7 and I am looking into putting aragonite into my sump to try to bring that level up a little bit. Is this a bad idea or should I just leave it alone. The fish seem happy and I have had several spawns. I was just hoping to bring there color out a little more.
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Re: PH level

Postby DJRansome » Sun Aug 23, 2020 2:15 pm

IDK if it will improve color, but it won't hurt to place crushed coral (same as aragonite and cheap) in your filter media containers where the water will be forced through the gravel.
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Re: PH level

Postby Funkster » Sun Aug 23, 2020 2:24 pm

I was hoping that it would bring the level up slowly enough that it wouldn't cause shock to the fish
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Re: PH level

Postby DJRansome » Sun Aug 23, 2020 2:35 pm

It may not bring the level up at all. I have had aragonite in some tanks and not others for 10 years...no change.

I started at 7.8. If you are starting at 7.0 you might get more of a change. Try a little at first and see how it goes.
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Re: PH level

Postby sir_keith » Sun Aug 23, 2020 7:59 pm

Let's try this again. Buffers, by definition, are ionic compounds in solution that affect the hydrogen ion concentrations (pH) of aqueous solutions. Since aragonite and other 'crushed coral' products are solids, they are, by definition, not buffers. They do, however, slowly release carbonate and bicarbonate ions into solution, which then act as buffers. As such, aragonite is a useful means of maintaining the pH of an appropriately buffered solution, but it is not an effective means of changing the pH of a neutral solution, because it releases carbonate salts into solution too slowly. To change the pH effectively, you must add an appropriate mixture of soluble carbonate and bicarbonate salts to the solution, the ratio depending on the final pH you'd like to achieve. One can buy pre-mixed blends of carbonate salts to do this; SeaChem Malawi/Victoria Buffer and Tanganyika Buffer are two examples of such mixtures. Once you have achieved the desired pH, aragonite and crushed coral help to maintain the pH at that level.

So, to your question: aragonite in your filter will not increase the pH, except painfully slowly, if at all. To increase the pH, add small amounts of an appropriate soluble buffer, such as SeaChem Malawi/Victoria Buffer, over time until the desired pH has been achieved. At that point, you can use Aragonite to help maintain the pH at that level, or not, as you wish, but I very much doubt that a bit of Aragonite in a filter will do much of anything at all. Because aragonite releases soluble carbonate and bicarbonate ions so slowly, you need a lot of it to be effective. All of my Tanganyika tanks are maintained at pH 8.8-9.0 by using SeaChem Tanganyika Buffer, added at the recommended dose at each and every water change, and an Aragonite substrate, typically 100 pounds per 100 gallons of water. Good luck! :thumb:

Wild-caught Tanganyikan featherfins, two years after acclimatization to water buffered as described above-

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Re: PH level

Postby DJRansome » Sun Aug 23, 2020 8:13 pm

What sir_keith has described has been my experience.

How do we explain fishkeepers who have a very low pH that report the limestone rocks or aragonite substrate changes their pH (and KH and GH) in a matter of days? Are they mistaken?
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Re: PH level

Postby sir_keith » Sun Aug 23, 2020 8:39 pm

DJRansome wrote:What sir_keith has described has been my experience.

How do we explain fishkeepers who have a very low pH that report the limestone rocks or aragonite substrate changes their pH (and KH and GH) in a matter of days? Are they mistaken?


No, because at low pH even small amounts of carbonate and bicarbonate ions that are released into solution from a solid substrate can have a measurable effect on increasing the pH of the solution. This effect becomes progressively smaller as the initial pH of the solution is increased. As you've noted, adding aragonite to a tank that already has an alkaline pH, 7.8 for example, doesn't do much of anything at all. Put another way: the titration curve for a buffered solution is not linear, it is sigmoidal, and whether you see an effect or not depends on where you are on the curve, specifically, the initial pH.
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Re: PH level

Postby ken31cay » Sun Aug 23, 2020 9:14 pm

sir_keith wrote:No, because at low pH even small amounts of carbonate and bicarbonate ions that are released into solution from a solid substrate can have a measurable effect on increasing the pH of the solution. This effect becomes progressively smaller as the initial pH of the solution is increased. As you've noted, adding aragonite to a tank that already has an alkaline pH, 7.8 for example, doesn't do much of anything at all. Put another way: the titration curve for a buffered solution is not linear, it is sigmoidal, and whether you see an effect or not depends on where you are on the curve, specifically, the initial pH.


+1 well said.
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Re: PH level

Postby DJRansome » Mon Aug 24, 2020 8:45 pm

pH=7.0 is not low? Would you expect OP to see an impact?
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Re: PH level

Postby sir_keith » Tue Aug 25, 2020 12:44 am

DJRansome wrote:pH=7.0 is not low? Would you expect OP to see an impact?


No to both. pH7 by definition is neutral; it corresponds to the dissociation constant of pure water.
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