Is there a need to buffer my water to 3dKH to prevent pH swings?

jaypeecee

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Hi Folks,

The above thread title is a question posed by Dennis Wong on his web site, the 2hr Aquarist:

https://www.advancedplantedtank.com/blogs/ph-kh-gh-tds/hardwater-softwater-decoded

The reply given is "There is absolutely no need to do so, unless you are doing specifically to accommodate livestock that favors a certain pH/KH value. Contrary to popular belief - low KH doesn't give rise to pH crashes without additional triggers. This is a remnant of ancient aquarium dogma".

Let's extract the essence of what Dennis Wong is saying and that is "low KH doesn't give rise to pH crashes without additional triggers". But, these triggers can, and do, occur. It's happened to me. I once bred German Blue Rams (GBRs). I had 41 juvenile fish in a 50 litre tank. One day, I measured the tank water pH and it had dropped considerably. I don't have the figure readily at hand. And, when I measured KH, it had also dropped significantly. Again, I don't have a figure readily at hand. But, at a push, I should be able to find it in one of my many aquarium logs. I remedied the situation by gradually adding sodium bicarbonate to raise KH and thus pH. I think this situation had been caused by the biological filter nitrification utilizing carbonate (for a supply of carbon) and its acidification of the tank water. Fortunately, not a single fish suffered in the process.

I aim to maintain my tanks at a minimum alkalinity/carbonate hardness of 4dKH.

JPC
 
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JoshP12

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I am actually currently debating with this inside. I do remineralize my water as my tap water comes out around .5 - 1KH ... I don't want to add potassium bicarbonate for ease of water changes, but I do ... and here are my thoughts.

KH measures carbonate hardness, which gives rise to some buffering capacity, we create acids every second, so we need some KH like you say @jaypeecee.

Water changes also replenish KH ... if we didn't need it Walstad wouldn't have added it to her substrate.

When I did my first tank upgrade from 5 gallon to 10 gallon, I also added miracle gro to the substrate and way to much seeing as how I had livestock which caused the tank to cycle and cycle hard - ammonia off the charts. I saw my pH crash.

If the nitrogen cycle is an additional trigger, well ...

Josh

PS I think maintenance is the key. If you have a "stable" system, you watch your plants, you watch your fish, you remove decaying matter, you water changes weekly and lots of it, you run purigen, I mean the tank will be clean, so your non-zero KH is really all you need ... but if you don't do any aspect of this ... it's safety?
 

Witcher

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JoshP12

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Hey @jaypeecee while I'm a fan of Dennis Wong approach in general, I'm afraid he may be completely wrong on this subject.



The additional trigger in this case may be carbonic acid (CO2 + water), while it's weak acid, I think at certain level it may cause the pH to fall dramatically if buffer will be depleted
https://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html

Right, but this additional trigger is not going to "harm" fish (due to the root of the change being gaseous in nature) and I think the point of the pH crash is that it harms the fish ... though I am now rethinking the effect that the concentration of H+ has on livestock ... could fish live in vinegar? I my vinegar comment may be treading into the difference between strong and weak acids etc ... and it may overcomplicate what we actually care about.

Josh
 

Witcher

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Right, but this additional trigger is not going to "harm" fish (due to the root of the change being gaseous in nature) and I think the point of the pH crash is that it harms the fish ... though I am now rethinking the effect that the concentration of H+ has on livestock ... could fish live in vinegar? I my vinegar comment may be treading into the difference between strong and weak acids etc ... and it may overcomplicate what we actually care about.

Josh

Some of the fish can live in the water with pH very close to vinegar acidity (pH 2.5):

Cardinal, neon, and emperor tetras (Cheirodon axelrodi, Hyphessobrycon innesi, Nematobrycon palmeri ), small South American characin fish often found in acidic blackwater rivers, have an unusual tolerance to sulfuric acid solutions of low pH. Most cardinal tetras withstand immediate transfer to water at pH 3.5 for an indefinite period. With gradual adjustment to further stepwise lowering of the pH, one individual survived at a pH of 3.1 for five weeks. This is by far the most acidic solution known to be tolerated for extended periods by any fish. The lower incipient lethal level (for 50% survival) is estimated to be about 3.35 for neon and cardinal tetras. On the other hand, common guppies (Poecilia reticulata ), a species generally considered to be highly resistant to environmental change, all died after 11 days at pH 4.75. Both guppies and tetras lose large amounts of body sodium on exposure to lethal pH's.

source: https://onlinelibrary.wiley.com/doi/pdf/10.1002/jez.1402010202
 

JoshP12

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Woah @Witcher!

That's very informative - thank you.

So, then I think the crux of this statement is, "what is a pH crash?"

Is it: a sudden drop in pH caused by gases? Salts (carbonates)? Just a liberation of H+ that is gradual?

pH "crashes" from drastic carbonate changes kill.

pH "crashes" from gases are ok, fish are much more likely to die from asphyxiation rather than the acidity (if we push it too much).

pH "crashes" from the liberation of H+ gradually ... uhhh ... well I think we have 2 categories: an induced nitrogen cycle (or decay) or a stable nitrogen cycle (complimented with steady rot/decay). In the induced, I wonder if it is just the ammonia which is the damage and NOT the pH crash ... the stable is well ... probably fine?

... so it really isn't the pH after all that is killing the fish, it is us (either our overgassing, our rediculus carbonate adding, or our poor cleaning or inability to provide a healthy environment :arghh::arghh:)

EDIT: But stress = a combination of everything ... so I am sure that the shift in H+ concentration does contribute a non-zero amount of stress ... just not as much as 1ppm of ammonia.

Josh
 
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jaypeecee

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Hi Folks,

I need time to digest your feedback. But I would add this - although we often refer to KH as 'carbonate hardness', this term is not strictly correct. KH should be known as 'alkalinity'. For more information, please take a look at the following excellent resource:

https://www.thekrib.com/Plants/CO2/alkalinity.html

Twenty years ago, The Krib used to be one of the de facto references for aquaria in general but, particularly, planted aquaria.

I'll be back later.

JPC
 

Wookii

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Interesting topic, and I’d like to know the answer as I’m looking to move to RO water.

The key takeaway for me in his article is:

Between 2- 6 dKH you can keep 97% of all commercial aquatic plants in optimal condition.

We know that aquarium soils buffer the KH down, so why risk hitting zero and seeing possible large Ph swings when injecting CO2, causing possible I’ll effects to livestock.

I guess the question I’m working around to is, what are the downsides of maintaining a KH of 3-4 prior to any soil buffering effect?
 

dw1305

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Hi all,
"There is absolutely no need to do so, unless you are doing specifically to accommodate livestock that favors a certain pH/KH value. Contrary to popular belief - low KH doesn't give rise to pH crashes without additional triggers.
I agree with him. It is back to pH not being a very useful measurement when you have very few ions in the water. I'd agree with @JoshP12 , if you have a drop in pH, accompanied by a large change in water chemistry, you are likely to have problems.

My opinion is that acidosis and fish death are both symptoms that something has gone wrong, they aren't cause and result.

cheers Darrel
 

jaypeecee

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It is back to pH not being a very useful measurement when you have very few ions in the water.

Hi @dw1305

Thanks for that, Darrel.

I suspect you're referring to pH meters struggling to read accurately in low ionic strength water? But, in the case that I described, there would have been plenty of calcium ions, to give just one example. If necessary, I'll try to find the log book for the tank that I was talking about. I (hopefully) will have recorded GH, KH and conductivity.

What I'm unclear about is - to what extent does a sudden drop in pH affect fish? In my case, they were juvenile GBRs - about 1cm in length. Is the 'pH crash' phenomenon a fallacy? Are we chasing a ghost? Stranger than strange!

JPC
 

dw1305

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Hi all,
I suspect you're referring to pH meters struggling to read accurately in low ionic strength water?
That is one problem, you can get around it <"by adding a neutral salt">, but there is a much more fundamental issue, which is that pH is both a log^10 value and a ratio.

As you get towards pure H2O (rather than the dilute solution of salts with H2O as a solvent, that we usually call water) the actual amount of ions declines and the addition of bases (H+ ion acceptors) or acids (H+ ion donors) needed to change the pH declines as well.

I'll simplify a little bit by ignoring the hydronium ion (H3O+), but when we just have H2O we have the <"self-ionization of water"> and 10^-7 H+ ions and 10^-7 OH- ions. We usually say that pure water is an electrical insulator, but that isn't strictly true, the self ionization gives a conductivity value of 0.055 microS. The pH is pH 7 because pH is the negative log of the hydrogen ion *concentration (*activity really) and we have 10^7 H+ ions.

When we add an ion it is either basic (left hand side of the periodic table) or an acid (right hand side), and as salt either basic (weak acid & strong base), acidic (strong acid & weak base) or neutral (strong acid & strong base etc.).

If we add a neutral salt (like NaCl, the salt formed from the reaction of a strong base Na and a strong acid Cl), as we add more salt the conductivity will rise, but the pH won't change, because we haven't changed the ratio it doesn't matter if we add one grain, one gram or 10 grams of NaCl .

If we start from H2O again, but in this case add a weak acid (like the <"(H2CO3) formed when CO2 dissolves)">, it doesn't matter how small that addition is the pH will fall. Same if we add a base, the pH will rise.

Normally we have a situation where we have a lot of different ions and the pH is defined by their ratio. If you have a basic solution, with a large excess of bases, it takes the addition of a lot of acids to change the pH. If we have a lot of buffering, it takes <"even more acid addition"> to burn through that buffering.

cheers Darrel
 

JoshP12

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Hey @jaypeecee,

Do you remember in your example:
1) the base KH
2) how long between water changes
3) if anything other than natural tank behaviour happened that day/few days before?

I use pH as a proxy - it tells me that everything is pretty much the same as yesterday or something has gone wrong.

Regarding: To what extent does the drop affect fish is something - I would think it is based on the nature of the drop: gas, salt, decay (in some ways the nitrogen cycle).

Then the argument becomes what "killed" the fish (since the context of pH crash is always the damage to fish health), the pH drop OR the root cause of the drop.

If your base KH was “lower” .5-1 and you hadn’t water changed (which would replace the carbonates) for a month, then I wouldn’t be surprised if the nitrogen cycle H+ byproduct bonded to all of your carbonates (I am not sure here if the bacteria actually use carbonates in the process - it sure feels like it when it plummets over night in mid cycle ... slight exaggeration, but if you put in lots of ammonia it will plummet) and as a result dropped your pH.

If you recently WC, then something had to cause the spike in acids - something rotting etc.

If you water changed and nothing not “normal” happened, then I am not sure what produced the acid.

Josh
 
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jaypeecee

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Hi @JoshP12

I found the tank log. :)

Like yourself, I was also using pH as a proxy. I'm kicking myself for not having measured KH as well. But, I was also keeping an eye on conductivity. It boils down to convenience. I have pH and conductivity meters so these figures were recorded. But, even then, I was lax. It all happened around Christmas 2018. Inconsiderate Rams! Conductivity was around 400 microS/cm and pH was 7.4 before the crash. Then, pH dropped to 5.95 and KH was zero. Interestingly, conductivity had risen to 457 microS/cm. As I said before, all buffering would have been removed by the nitrification process. I don't think we need to look any further for an explanation of the likely cause. I just wasn't expecting this to happen. It taught me a lesson. On the basis that KH couldn't have dropped any lower and had I not intervened, the pH would have probably continued to drop even lower.

But, now, returning to the title of the thread, I would argue that low KH + trigger can lead to problems. And, as I have unintentionally demonstrated, these triggers can, and do, occur. Therefore, in order to prevent a pH crash, I think it's very advisable to ensure that alkalinity needs to be at least 3dKH. I always aim for 4dKH.

JPC
 

Hanuman

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As you get towards pure H2O (rather than the dilute solution of salts with H2O as a solvent, that we usually call water) the actual amount of ions declines and the addition of bases (H+ ion acceptors) or acids (H+ ion donors) needed to change the pH declines as well.

I'll simplify a little bit by ignoring the hydronium ion (H3O+), but when we just have H2O we have the <"self-ionization of water"> and 10^-7 H+ ions and 10^-7 OH- ions. We usually say that pure water is an electrical insulator, but that isn't strictly true, the self ionization gives a conductivity value of 0.055 microS. The pH is pH 7 because pH is the negative log of the hydrogen ion *concentration (*activity really) and we have 10^7 H+ ions.
Sorry Darrel just had to say this:
I am 100% sure it's pure chemistry but my brain just melted.
 

dw1305

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Hi all,
I am 100% sure it's pure chemistry but my brain just melted.
I think I understand it, but I've had the same issues. From <"What's the deal with KH/Alkalinity">:
That is often the issue. I'm not a chemist and I had to get people who understood the chemistry to explain it to me (in terms I could understand) before I could join up all the dots. From a personal point of view, I think I found pH and buffering the most difficult concepts, because even though I knew what the definitions were I didn't understand what they meant in practice.
Stable pH only exists in very heavily buffered water. As you approach pure H2O pH becomes less and less meaningful. In soft waters pH will always be a movable feast, and you can't extrapolate from sea water or Lake Tanganyika to soft water. I look on changes in pH in another way, I just say "does this change in pH reflect a large change in the chemistry (number of ions) in the water?"
cheers Darrel
 

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