PH vs KH

[_Maq_]

However I feel that the hobby has fallen in love with RO water just as people drink bottled water when tap water is fine.

I think the primary concern is bicarbonates. Hard water usually comes with high bicarbonates. They are unwelcome in themselves plus they push pH too high. Diluting such water with RO water is a sound approach.
On the other hand, I admit I haven't detected any negative influence of sulfates & chlorides. As for corresponding content of magnesium and calcium - i.e. water hardness - I do believe some species prefer them in the lower range.

 

[Oldguy]

I do believe some species prefer them in the lower range.

I agree with high pH being problematic, hence I nip my pH down with dil HCl. It is difficult to add nitrates without it being a potassium source , hence my use of Ca & Mg nitrates. Levels of these Gp II's are not high, perhaps yielding moderately hard water.
Life might be simper if aquarists could obtain a permit for limited amounts of ammonium nitrate. Must try and acquire some friends in low places. Lol.
Perhaps many of us, self included, try and grow plants in the same tank that have polar requirements.

 

[dw1305]

Hi all,

I think the primary concern is bicarbonates. Hard water usually comes with high bicarbonates. They are unwelcome in themselves plus they push pH too high.

I agree with high pH being problematic, hence I nip my pH down with dil HCl

In which case (the HCl) you've lowered the (<"alkalinity, temporary hardness or carbonate hardness">), the dKH by converting <"some of the TIC"> from <"HCO3- to CO2">.

Perhaps many of us, self included, try and grow plants in the same tank that have polar requirements.

Certainly <"my view">. I'm very much <"grow what wants to grow "> in your tank conditions. It is the <"same for fish">, keep fish that like your tanks. It might not be very exciting but it saves a lot of heartache.

cheers Darrel

 

[hax47]

Are you suggesting that plants are better off with higher levels of electrical conductivity aka TDS in general? If so, I can’t see how that can be true given that all our plants are from waters with relatively low overall mineral content (low TDS) compared to what we usually offer in our aquarium

I'm currently reading Diana Walstad's book, and she claims that even plants with softwater habitats could do better under hardwater conditions. She conducted tests using Bacopa caroliniana and Sagittaria graminea, two supposed softwater species. According to her, while these species tend to perform better in soft water than hardwater plants, they can still benefit from a higher mineral content. Not sure how much one can generalize from two species, but sounds reasonable unless pH/KH is too high.

 

[dw1305]

Hi all,

I'm currently reading Diana Walstad's book, and she claims that even plants with softwater habitats could do better under hardwater conditions.

I'm a <"great Diana Walstad fan">, but I'm pretty sure that isn't true for all "soft water" plants. Most <"easy plants"> will be pretty tolerant (that is why they are "easy"), but even some of these, <"like Rotala rotundifolia">, don't do well with high dKH values - <"Choosing Aquarium Plants For Soft And/Or Hard Water">

@Roland has decoupled dGH (hardness) and dKH (alkalinity) and he grows many difficult plants at <"5 - 6 dGH, but 0 dKH">.

An <"objective criticism"> of Diana Walstad would be that she had to have high carbonate hardness originally, because <"she didn't change any water">, and that meant carbonates could be exhausted (in softer water) by nitrification <"Does depleted KH stop the nitrogen cycle?"> leading to <"old tank syndrome">.

She started from the position that you needed high alkalinity, and to some degree, fitted the "facts" around that.

cheers Darrel

 

[Andy Pierce]

I agree with high pH being problematic, hence I nip my pH down with dil HCl

In which case (the HCl) you've lowered the (<"alkalinity, temporary hardness or carbonate hardness">), the dKH by converting <"some of the TIC"> from <"HCO3- to CO2">.

You will also have noticed after adding the HCl that the pH does not stay 'nipped down' but rather rises again to a pH value only slightly lower than it was before you added the acid. This is because (and this is mostly true) when you add the HCl the HCl is converted by the bicarbonate to carbonic acid/CO2, and as the CO2 escapes to the atmosphere, it takes the carbonic acid away with it. Essentially, your acid has evaporated.

 

[dw1305]

Hi all,

You will also have noticed after adding the HCl that the pH does not stay 'nipped down' but rather rises again to a pH value only slightly lower than it was before you added the acid.

Yes, it is back to <"strong and weak acids"> and <"weak acid / weak base buffering">. I'm cr*p at explaining this, but here goes again.........

HCl is a "strong acid" and completely disassociates into a proton (H+) and chloride ion (Cl-). Acids are defined as <"proton donors"> and we've added H+ ions and the pH falls.

It is the <"same reaction"> as when we drip HCl onto a limestone, but in that case we can see the rock dissolve and the CO2 bubble off. When all the H+ ions are neutralised (by the CO3-) we have CaCl2, H2O and evolved CO2.

We still have the <"same level of Dissolved / Total Inorganic Carbon ((D)TIC)"> in the "new water" with its composition being dependent upon the same factors as any other water.

<"CO2, 2HCO3 & CO3 is the buffered system"> (that we've intruded on with our addition of HCl), with the pH level being set by the level of atmospheric CO2 <"Global Monitoring Laboratory - Carbon Cycle Greenhouse Gases">.

cheers Darrel

 

[Oldguy]

does not stay 'nipped down'

with the pH level being set by the level of atmospheric CO2

That's why I don't I measure pH in these types of situations. My tap water has very low temporary hardness and the pH is due to 'other factors' at the treatment works.
I think it saves me a bit of CO2 on injection especially if the tap water pH is due to OH ions. (I also leave it marry with the rain water over night)
I also think that pH measurements of typical aquarium water are a hiding to nothing. Just about every thing is buffering in some way and the solutions are very very dilute.
Hopefully the injected CO2 is there mainly as undissociated gas dissolved in water, as indicated by a drop checker, which I do not use. If the fish are active; the plants grow; and the snails keep their shells, if a bit thin, and multiply, then the tight rope is being walked.
Others no doubt will have their own views.

 

[dw1305]

Hi all,

and the pH is due to 'other factors' at the treatment works.

So in the case of <"sodium hydroxide (NaOH) injection"> and hydrochloric acid (HCl) addition, we are into a <"strong base & strong acid interaction"> and that makes it a lot more straight forward, because everything is in solution and we don't have any buffering.

In this case we have a Na+ ion and an OH- ion in solution. The "OH-" is a proton acceptor (a base), and an H+ (proton donor) added 1 : 1 to a OH- (proton acceptor) gives us ta da ........... H2O, the neutral aqueous salt we call "water".

We also have an Na+ and a Cl-, NaCl is "salt" and <"a neutral salt"> and highly soluble, so both Na+ and Cl- ions remain in solution, but don't effect the pH.

I also think that pH measurements of typical aquarium water are a hiding to nothing. Just about every thing is buffering in some way and the solutions are very very dilute.

I definitely <"agree with that">.

If the fish are active; the plants grow; and the snails keep their shells, if a bit thin, and multiply, then the tight rope is being walked.

I honestly believe that <"the Snail shell index"> is the way forward for low tech keepers.

A bit like the <"Duckweed Index"> (using Amazon Frogbit (Limnobium laevigatum)) you can use it across a whole range of water hardness.

• Can't keep any snails alive with their shells rapidly disintegrating? You have soft, acidic water.
• Your Ramshorn snails never get very big? and <"they are really pale">? You have soft water, that is sometimes acidic.
• You can keep MTS, Ramshorns etc. but Rabbit and <"Assassin snails"> show shell attrition? You have water that is usually alkaline, but isn't particularly hard.
• You can keep all types of snail and their shells never show any sign of attrition, even in the oldest whorls? You have <"Lake Tanganyika">

cheers Darrel

 

[hax47]

I also think that pH measurements of typical aquarium water are a hiding to nothing. Just about every thing is buffering in some way and the solutions are very very dilute.

I have been wondering what molecules besides bicarbonate could act as buffers in an aquarium. For any buffer, the effective buffering range is 1 pH unit on either side of the pKa (the negative logarithm of the acid dissociation constant), and it also has to have some substantial concentration to have significant buffering capacity/effect (bicarbonate is an exception from the ±1 pH buffer range because the acid part of the buffer is a volatile gas). One obvious candidate would be the phosphate buffer, having one pKa of 7.21 (besides two other ones around 2 and 12, both out of a realistic range). But its realistic concentration, except in very soft waters with high PO4 concentration, should be close to negligible compared to bicarbonate buffer capacity (1 ppm PO4 is ~10 micromol/l, 1 dKH hardness equals ~ 356 micromol/l HCO3-). Organic compounds could have pKas in the right range, but I don't know if the concentration of those is comparable to the bicarbonate.

 

[dw1305]

Hi all,

One obvious candidate would be the phosphate buffer, having one pKa of 7.21 (besides two other ones around 2 and 12, both out of a realistic range). But its realistic concentration, except in very soft waters with high PO4 concentration, should be close to negligible compared to bicarbonate buffer capacity (1 ppm PO4 is ~10 micromol/l, 1 dKH hardness equals ~ 356 micromol/l HCO3-).

Traditionally <"Aquarium buffers"> are phosphate buffers, either potassium (K) or sodium (Na) salts.

cheers Darrel

 

[MichaelJ]

However I feel that the hobby has fallen in love with RO

And for good reasons. If your tap water is very alkaline (high KH), there is really no other good permanent and natural way of lowering the alkalinity /pH than using rain water or RO water. If your KH is already low, you can use peat moss or sphagnum to lower it additionally, but otherwise that is usually not practical either. Adding chemicals to lower your KH/pH is nothing better than putting a band-aid on a gunshot wound - at least that was the case for me when I went down that rabbit hole some years ago.

As far as general mineral content are concerned Calcium, Magnesium and the Sulphates and Chlorides we often take on as collateral from fertilizers and remineralization, I am less concerned of adverse effects for the plants, but I fail to see how inordinate or elevated levels can be beneficial either, and certainly many species will prefer lower levels. For years I was under the impression that certain plants actually preferred a higher Ca/Mg content such as Vallisneria and certain Echinodorus species and wouldn't thrive in waters with low levels of Ca and Mg. The plants we categorize as being Easy are merely plants that tolerate higher levels of minerals, higher alkalinity (KH) thus higher pH, but they will all benefit from lower alkalinity and moderated mineral levels... and yes, extra CO2.

On a side note; In order to rid ourselves of the ambiguity, we should much rather use the term low alkalinity with elevated/higher mineral content, rather than soft water with elevated/higher mineral content.

Cheers,
Michael

 

[dw1305]

Hi all,

Adding chemicals to lower your KH/pH is nothing better than putting a band-aid on a gunshot wound - at least that was the case for me when I went down that rabbit hole some years ago.

I'd definitely agree with that. It is the <"tea / coffee analogy">.

@Oldguy 's example is slightly different, because it doesn't involve buffering and he can neutralise the hydroxide (OH-) ions with a small addition of protons (H+ ions).

However I feel that the hobby has fallen in love with RO water

Yes it has, and I agree with @MichaelJ there are reasons for this. Personally, if I couldn't use rainwater? I would <"use our tap water"> and keep different plants and fish. I'll be honest, I have <"severe reservations about tap water"> (of any hardness) and it isn't a route I would go down voluntarily.

cheers Darrel

 

[MichaelJ]

I would <"use our tap water">

use our tap water ... This got some really fascinating Darrel / @dw1305 posts (as always)! Some 13 years old, but still valid I suppose... Turns out his whole yard revolves around securing endless supply of rain water for his tanks

I wish I could do that. Unfortunately, collecting rain water in Minnesota would only work for part of the year. In the winter it would be snow.... but that snow... I sampled it last winter and the TDS of the snow melt was down around 7 ppm.


Cheers,
Michael

 

[dw1305]

Hi all,

Turns out his whole house revolves around his endless supply of rain water

Pretty much.

Some 13 years old, but still valid I suppose..

No, only 11 years old.

I maintain a series of, what you might call, <"faith positions">. but within reason <"many of them"> have <"become more mainstream over time">. So here <"is a prediction">, I predict that a company will go down the <"Secret Ingredient Soup"> route at some point in the future.

cheers Darrel

 

[palcente]

I have a small problem where plants stunts then create healthy shoot from that stunted tip then stunt again etc..

I bet my left nut that you are not dosing your macros correctly.

 

[Gorillastomp]

I bet my left nut that you are not dosing your macros correctly.

What do you mean by not correctly dosing macros ?

I was dosing daily an aio fertilizer when my ph was down to 6.8-6.9.

From testing i had something like
28 ppm NO3, 4 ppm PO4, 30 ppm K and this thenone i dont remeber correctly FE was 0.28 ppm or 2.8 ppm in tank after severals weeks.

 

[MichaelJ]

No, only 11 years old.

It just felt more like 13 years... anyway, if I would be claiming using base-8 notation (octal) I would be correct though - but I won’t.

I maintain a series of, what you might call, <"faith positions">. but within reason <"many of them"> have <"become more mainstream over time">. So here <"is a prediction">, I predict that a company will go down the <"Secret Ingredient Soup"> route at some point in the future.

Those all are classic UKAPS postings!

Cheers,
Michael

 

[_Maq_]

I'm currently reading Diana Walstad's book

Might be useful as long as she cites hard, exact facts. The rest is just her speculation...

fitted the "facts" around that

... violating all scientific rules. She quotes sources selectively to fit her weird theories, and her "experiments" obviously serve the same purpose. She should be celebrated as an example of anti-scientist.

You will also have noticed after adding the HCl that the pH does not stay 'nipped down' but rather rises again

That's why it's useful to keep in mind that the correct term for alkalinity is acid neutralizing capacity.

Just about every thing is buffering in some way and the solutions are very very dilute.

If you work with sparsely mineralized water - like I do - you'll see very different results.

I have been wondering what molecules besides bicarbonate could act as buffers in an aquarium.

Humic acids. They are present in significant amounts even in drinking water. They are reported to be difficult to remove completely during water processing.

 

[palcente]

What do you mean by not correctly dosing macros ?

I was dosing daily an aio fertilizer when my ph was down to 6.8-6.9.

From testing i had something like
28 ppm NO3, 4 ppm PO4, 30 ppm K and this thenone i dont remeber correctly FE was 0.28 ppm or 2.8 ppm in tank after severals weeks.

And you know these are the right quantities for your tank how? I can tell you this would not work in my tank, plants would stunt by Wednesday if I front loaded this little over the weekend... They clearly do not work in your tank - I saw your plants...

Focus on the plants, not some arbitrary numbers...