Permanently lowering KH, questions for chemistry wizard

[Hufsa]

Disclaimer/warning!
This topic discusses the usage of strong acids. I do not wish for anyone to take me posting this inquiry as endorsement or encouragement.
Anyone handling strong acids should only do so with the appropriate knowledge and safety gear. If you do not have respect for strong acids or bases you should not be handling them. More concentrated does not mean better.
If you are a beginner this is not something you should be messing with at all and this is not the way to fix any problems you may be having (please post a thread on the forum and you will receive help).

Whew.
With that said, good evening everyone 🙂
Something I have been thinking about for a while is various options for permanently lowering KH.
Im not looking to lower KH to fix any problems. Since RO is not currently an option for me, lowering my KH a little bit would take my otherwise perfectly good tap water much closer to ideal parameters for certain species of shrimp and plants.
Some may already have heard of lowering KH with Hydrochloric Acid (HCL).
This adds Chloride which is not directly harmful but less useful for a planted tank.
I was looking into other acids that could potentially be used to lower KH and that add actual plant nutrients.
I quickly realized that while they add useful ions for our plants, some of them are also much more dangerous to handle.

I have come across two hydroponic products for the lowering of PH (KH) that look like they could be used for this purpose.
One contains 3% nitric acid and the other 10% phosphoric anhydride.

My main question is, if I was looking to lower the KH by 2 degrees, roughly how many ppm of NO3 and/or PO4 would I be adding? My tap KH comes from being "filtered over Marble", so from what I understand will be almost all from CaCO3.
My concern would be whether this amount would add so much nutrients it essentially becomes not an option for aquariums, lets say beyond EI targets?

And secondly, are these percentages ok for a layperson to handle, using chemical resistant gloves, safety glasses, a face shield and a long pipette?
I think it is a terrible idea to add strong acids directly into an aquarium, so they would be added to a 200 liter barrel where I prepare my water change water.

I also seen mention of citric acid, but I am wondering if extensive usage of this to lower KH would lead to unwanted algae or bacterial blooms?


Greatly appreciate any help from a chemistry wizard to work out the calculations and advise on the safety aspect 😊

 

[_Maq_]

I suggest sulfuric acid. But hydrochloric acid would work as well. (Frankly, I don't see where certain fear of chlorides comes from. Certainly not a problem in amounts we're about to discuss.)
Don't - I repeat - don't use citric acid for this purpose. I'll try to explain. Citric acid is an organic compound, easily degradable. That means, it's a delicacy for microbes. Degradation means oxidation and the end-product (after some white bacterial bloom) is CO2 in equilibrium with HCO3-.
Sulfuric acid, on the other hand, will effectively replace bicarbonates with sulfates. It can be calculated, in theory, but careful approach is necessary, anyway. Are you friendly with molar calculations? Do you know the molar amount of bicarbonates in your water? From that the amount of a strong acid (H2SO4 or HCl) could be derived. ---- But still, though I'm capable of making these calculations, in practice, whenever lowering pH with H2SO4, I make a diluted solution and add the acid with pipette as long as necessary to reach the desired pH. There's still a great uncertainty there, though, because tanks possess some hardly explicable resiliency against pH changes. In short, you'll have to try yourself.

 

[Hufsa]

I suggest sulfuric acid. But hydrochloric acid would work as well. (Frankly, I don't see where certain fear of chlorides comes from. Certainly not a problem in amounts we're about to discuss.)

I dont think Chlorides are really a problem, its more coming from a nerdy desire to min-max as much as possible 😁

Don't - I repeat - don't use citric acid for this purpose. I'll try to explain. Citric acid is an organic compound, easily degradable. That means, it's a delicacy for microbes.

Yeah this is sort of what I was guessing might be a problem with Citric. Add a ton of organic acid to something with as much microbes and algae spores as our tanks = recipe for a tasty buffet indeed

Degradation means oxidation and the end-product (after some white bacterial bloom) is CO2 in equilibrium with HCO3-.

I dont have any background in chemistry so much of what I know I have just learned through the hobby, my grasp on KH and PH is currently tenous at best.
Are you saying in addition to the first problem with citric acid, the second problem is that its not a permanent lowering of the KH?

Sulfuric acid, on the other hand, will effectively replace bicarbonates with sulfates.

Sulfuric is an option too, I suppose from a min-maxing perspective would be slightly preferable to HCL just because plants are more tolerant of sulphates than chlorides.

It can be calculated, in theory, but careful approach is necessary, anyway.

Yes the final dosing will have to be subjected to actual practical tests on my water, I am anticipating a bit of trial and error involved in getting it just right and I am planning to do the testing well away from the actual aquarium.
What I wanted to know was how much NO3 and PO4 I would be looking at, I would prefer not to buy these PH adjusters only to find out they are not suitable because they add way too much. I could test to see what readings I get but that runs into the issue with reliability of Nitrate tests and I would rather have the math to back me up first.

Are you friendly with molar calculations? Do you know the molar amount of bicarbonates in your water?

Unfortunately no 🙁
I only know that the KH comes from marble and that the tap water report says that the water contains about 21 ppm Ca. Can it be calculated from this?

 

[MichaelJ]

I only know that the KH comes from marble and that the tap water report says that the water contains about 21 ppm Ca

Hi @Hufsa a total amount of 21 ppm of Ca is not much really. Assuming this all comes from CaCO3 your KH is just a smidge under 3 - even lower if not. Did you measure your KH with a kit?
Assuming its very low already, it wont take much to slash a degree of KH or two. Alternatively you could filter over peat moss 🙂


Cheers,
Michael

 

[_Maq_]

plants are more tolerant of sulphates than chlorides.

Exactly! This is some belief/opinion/scientific fact which I don't know where it comes from. What I do know for sure is that in general, plants take up much much more chlorides than sulfates, not for assimilation but for maintaining ionic balance of internal fluids.

Are you saying in addition to the first problem with citric acid, the second problem is that its not a permanent lowering of the KH?

Yes. I almost forgot to stress that: It does not decrease permanently the bicarbonate content (alkalinity).

What I wanted to know was how much NO3 and PO4 I would be looking at

Both HNO3 and H3PO4 are less recommendable because they contain key nutrients. In addition, HNO3 is fuming (more than HCl) and a degree more dangerous than the others. Phosphoric acid is fine, but we don't want too much phosphorus in our tanks, do we?
Interestingly enough, if I want to lower pH and alkalinity, I dose not nitrates but ammonium! Nitrification "eats" bicarbonates and lowers pH accordingly, quite mightily.
You'll need 1 dl [deciliter] of strong concentrated mineral acid for more than a year, I estimate.

tap water report says that the water contains about 21 ppm Ca. Can it be calculated from this?

Unfortunately, no. If I remember correctly, your water processing plant adds sodium bicarbonate. Merely from the amount of calcium you can't tell how much of it dissolved in water as a chloride, sulfate, or carbonate. And also Na, K & Mg can be present as solutes of all these salts. Alkalinity, bicarbonate content, or acid neutralizing capacity are the terms which relate directly to KH.
In any case, you'll have to make a stock solution of diluted H2SO4, I'd imagine 0.1%, and you can add it by milliliters next to the outflow of your filter. Then wait, and measure pH. Usually, if it drops by 1 degree, you'll learn on the next day that half of that decrease has been lost. Possibly. Trial and error. Good luck.

 

[Geoffrey Rea]

Previous thread:

Be safe kids.

You’ll have @dw1305 writing in bold again.

 

[MichaelJ]

Hi @_Maq_ Would a tiny bit of Seachem Adic Buffer be an option (KH -> CO2) for @Hufsa, say prepared in a WC container ? I believe its NaHSO4 which of course adds sodium.

Cheers,
Michael

 

[_Maq_]

I believe its NaHSO4 which of course adds sodium.

It works in the right direction. NaHSO4 is a choice of safety, you don't have to handle sulfuric acid. When in solution, it's a weaker acid compared with H2SO4. However, adding sodium is hardly a positive move.
Most annoyingly, there's the 'Seachem' price in it. If you insist on sodium bisulfate, you can get it much cheaper in shops specializing in ponds & pools. Most 'pH-minus' agents are just NaHSO4.

 

[Hufsa]

Previous thread:

Be safe kids.

You’ll have @dw1305 writing in bold again.

I had that post from Darrel in mind when I was writing the original post. Safety is #1.
I thought it would be best to ask about these products from people who know chemistry before I even consider going out and getting anything.

Hi @Hufsa a total amount of 21 ppm of Ca is not much really. Assuming this all comes from CaCO3 your KH is just a smidge under 3 - even lower if not. Did you measure your KH with a kit?
Assuming its very low already, it wont take much to slash a degree of KH or two. Alternatively you could filter over peat moss 🙂

Yes its not a lot, 21 ppm of Ca is what the water treatment plant states, and this seems to work out to 2,9x degrees KH or something like that in the rotala calculator.
When I use a JBL liquid KH test it comes out to juuust about 3 degrees, so this seems to match up.
I would only be looking to remove 2 degrees KH, not because I think 0 KH is inherently dangerous but because I have gotten the impression that having "unreacted" strong acid in the water would be a very bad thing.
Please someone correct me if that is wrong. So the last ~1 degree KH would be intentionally left behind to ensure that everything has reacted fully.

Exactly! This is some belief/opinion/scientific fact which I don't know where it comes from. What I do know for sure is that in general, plants take up much much more chlorides than sulfates, not for assimilation but for maintaining ionic balance of internal fluids.

Hm I thought I had this from Marschner but quick examination I cannot find it again. Its possible I just picked it up somewhere along the way. Some of the basis would be that Sulphate is a macro nutrient, also plant requirement for Sulphate is ten times more than Chloride. I think many people might then assume (correctly or incorrectly) that it would therefore "be better" to have more Sulphate than Chloride.

Yes. I almost forgot to stress that: It does not decrease permanently the bicarbonate content (alkalinity).

Well thats two complete dealbreakers for Citric then 🙂

Both HNO3 and H3PO4 are less recommendable because they contain key nutrients.

Less recommendable? I am going to be adding NO3 and PO4 to my tank anyway, so if you dont take into account the safety aspect of this whole thing then surely them adding key nutrients is a bonus?
That is why they are used for hydroponics?

In addition, HNO3 is fuming (more than HCl) and a degree more dangerous than the others.

Noted, fumes more, and is it more caustic also?

Phosphoric acid is fine, but we don't want too much phosphorus in our tanks, do we?

I would have to use relatively less of the phosphoric acid, this is one of my reasons for asking for clarification on how many ppm would be added.

Unfortunately, no. If I remember correctly, your water processing plant adds sodium bicarbonate.

They add NaOH not NaHCO3

 

[_Maq_]

They add NaOH not NaHCO3

Yes, but then NaOH reacts with CO2 to form (bi)carbonate.

Noted, fumes more, and is it more caustic also?

As far as I know, yes. Strongly corrosive, oxidizing agent. In fact, I keep dozens of various chemicals at home, including all mentioned mineral acids, except nitric acid. This one I've evaluated as too dangerous for me.

I have gotten the impression that having "unreacted" strong acid in the water would be a very bad thing.

Acidity is in fact concentration of H+ ions (protons). Par example, H2SO4 dissociates in water to 2 [H+] + [SO42-]. It does not matter where the protons come from, it's always just protons and what matters is their number, their concentration. If there are bicarbonates in water, they react with protons: [H+] + [HCO3-] == [H2O] + [CO2]. This reaction may go in both ways, depending on proton concentration. So, if you add strong acid to your tank, CO2 concentration increases temporarily at the cost of HCO3- concentration ('carbonate hardness'). CO2 above normal content given by partial pressure of CO2 in the air then dissipates out of water. What remains is the same concentration of CO2 but lowered concentration of HCO3-, which is what you aim for.

 

[dw1305]

Hi all,

You’ll have @dw1305 writing in bold again.

.....and UPPER CASE.

cheers Darrel

 

[MichaelJ]

I would only be looking to remove 2 degrees KH, not because I think 0 KH is inherently dangerous but because I have gotten the impression that having "unreacted" strong acid in the water would be a very bad thing.

That is sort of my impression as well. I remineralize my RODI water to a KH just around 1.0 for various reasons including the fact that natural (very)soft water ways tends to have very low but above zero KH and measuring pH with our test kits at zero KH is problematic at best.

EDIT: was linking to the wrong post;

Cheers,
Michael

 

[sparkyweasel]

you'll have to make a stock solution of diluted H2SO4,

Or buy it already diluted, which would be a bit safer.

 

[Wookii]

When I use a JBL liquid KH test it comes out to juuust about 3 degrees, so this seems to match up.

Is that measuring your tank water @Hufsa, or your tap water. A mature tank will often reduce the KH from organic acids produced (though I know you normally do fairly large water changes).

Have you tried adding humic/fluvic acids? You can get it from products such Easy Life Catappa X, or Microbe Life Bio-CO2, which are essentially concentrated extracts, or by adding botanicals directly to your tank (though you will get tannins resulting form that, at least temporarily). I can't comment on how much they might reduce the KH, but at least they are also beneficial to you tank and livestock as a side bonus.

 

[Hufsa]

Is that measuring your tank water @Hufsa, or your tap water. A mature tank will often reduce the KH from organic acids produced (though I know you normally do fairly large water changes).

That is tap water that was tested indeed. I can test the KH again before the next water change to see if it has dropped any, ill dilute the test to 0.5 degree steps otherwise im not sure a reduction would show up.
I will be somewhat surprised if the tank values differ much, my tank runs "fairly clean" with low stocking and inert substrate, plus those large water changes as you have mentioned.

Have you tried adding humic/fluvic acids? You can get it from products such Easy Life Catappa X, or Microbe Life Bio-CO2, which are essentially concentrated extracts, or by adding botanicals directly to your tank (though you will get tannins resulting form that, at least temporarily). I can't comment on how much they might reduce the KH, but at least they are also beneficial to you tank and livestock as a side bonus.

I havent tried adding any humic/fulvic, but I do have both Humic and Fulvic Acid powder on hand. My main concern with doing it "the biological way" if you can call it that is I dont want fluctuations in the KH.
I think a slightly less optimal but stable KH is likely to be better than a KH that jumps up and down, so any attempted adjustment to KH would have to be in the water change barrel before it sees the tank, and needs to be a process that is more or less done and stabilized in a couple of days max. I would also prefer "the result" to be stable over time if that makes sense, so that the tank water stays close to the values of the water change water.

I appreciate that we are discussing all the options here and it helps me get a well thought out overview on all the alternatives (still including the likely option of not doing anything to KH at all of course),
but I would still very much like a specific answer to my two main questions;

Are solutions of 3% nitric acid and 10% phosphoric anhydride diluted enough to be safe to handle with precautions?,
and
What sort of ppm addition of nutrients are we looking at if one were to lower KH by 2 degrees using those two acids?

Maybe I can try for a cheeky tag of the half blood prince
@X3NiTH

 

[_Maq_]

A mature tank will often reduce the KH from organic acids produced

These acids work rather differently, keeping some sort of equilibrium. See above my tractate on citric acid.

I dont want fluctuations in the KH.

I believe the strongest eater of alkalinity is nitrification. If you fertilize with urea/ammonium, decrease in bicarbonates is inevitable and remarkable. With that, pH falls down, as well.

Are solutions of 3% nitric acid and 10% phosphoric anhydride diluted enough to be safe to handle with precautions?,

Yes.

What sort of ppm addition of nutrients are we looking at if one were to lower KH by 2 degrees using those two acids?

Molar equivalent of 2 °dKH in bicarbonates (43.6 mg/L) is 44.3 mg/L nitrates = 45 mg/L nitric acid. [mg/L is the same as ppm.]
Phosphoric acid is more difficult to calculate because it's a triprotic acid (H3PO4 - three protons) and degree of dissociation depends on pH. In fact, phosphoric acid too is a source of alkalinity.
You're obviously preferring to stick to acids you've got but I've already told you that sulfuric or hydrochloric acids are the way to go.
Humic & fulvic acids do work, of course, but the results are incalculable and unstable, they too discolor the water, and impurities are a source of organic pollution. I've labored with them as well as with peat extract and the results were not beneficial.

 

[X3NiTH]

If I were targeting for nutrition and reducing KH I would be using Phosphoric Acid to reach a desired amount of P needed for the week between waterchanges in combination with Sulphuric Acid to target the remainder amount of alkalinity to be reduced.

You could use Hydrochloric Acid and Nitric Acid also but these are both fuming agents and extra precautions need to be taken beyond skin protection.

I think it’s easier/safer to begin with a demineralised water source and remineralise either being RO or Rain water, obviously this can be impractical for larger aquariums either being an expense for producing RO or enough storage capacity for Rain water.

🙂

 

[John q]

Fantastic thread. However why folks would contemplate adding sulphuric acid or phosphoric acid to there set ups is beyond me.

 

[KirstyF]

Fantastic thread. However why folks would contemplate adding sulphuric acid or phosphoric acid to there set ups is beyond me.

I think it’s to lower KH John. 😉

And why would they want to do that I hear you ask!

Maybe because they want to see what response they get from their plants by doing so.
Maybe they have plants that ‘typically’ do well in softer water and they wish to test that hypothesis.
Maybe just cos they wanna!

As a hobbyist who gets as much pleasure learning what plants do and how and why, as I do in making something lovely, I can totally see why folks would want to push boundaries. With the appropriate precaution taken, it’s a great way to learn…no?

 

[John q]

With the appropriate precaution taken, it’s a great way to learn…no?

Absolutely mate,not arguing with that. Can I suggest folks that want to experiment do it without live stock regardless of "safe" precautions.