High PO4 influence on KH

[charlie]

Hi Tom, in your EI article you mentioned high PO4 levels( excess of 5-10 PPM) can have a influence on th KH, my question is how does it impact the KH ?
Regards

 

[Tom Barr]

They have used PO4 for water treatment, mostly corrosion control in tap.
I'm not sure what the ppm's are or the chemicals are that are used.
It would take a great deal to act as a buffer. KH2PO4 is very slightly acidic, so if might make you think there's less KH than there really is, hence fooling you to think the pH/Kh chart is correct and you think there's more CO2 ppm than is really there.

I have no evidence however.
Inorganic chemist and some pkA's could tell you how much of an effect it might have.
I looked it up and discussed many years ago, I honestly forget off hand right now.

Might look it up in a chem text book.

Or ask someone here who's got nothing better to do
I know someone here loves chem and would not mind.

Still, at less than 10ppm, I doubt there's much effect.

Regards,
Tom Barr

 

[ordloh]

Really difficult to calculate since CO2 and other acids are variables and go up and down all the time in an aquarium. Can be done with some big assumptions. Assuming your aquarium water is pure water with pH 7 and also assuming that dissociation to H3PO4 and PO4 -3 is negligible (Kb of H2PO4- is 10^-12 and Ka of HPO4 2- is around 10^-13, we don't need to bother with them in the aquarium since the pH is never out of 5-8), adding 5e-5 M of phosphate in the form of KH2PO4 will result in a pH of 5.76
Of course the dissociation is less in an acidic solution, unfortunately CO2 and all the organic acids in our aquariums are weak acids so all the equilibriums will be pushing each other back and forth so it’s really hard to calculate. I might try later but I’m not too keen tbh lol.

 

[Philosophos]

The fact that I don't know the answer to this question sort of annoys me. Buffering questions pop up all the time and most people are just left shrugging. I'm downloading a textbook that should give some answers; it'll be done by tomorrow. I'm going to do my best to learn some of this, and perhaps write on the subject a little bit.

-Philosophos

 

[Tom Barr]

Really difficult to calculate since CO2 and other acids are variables and go up and down all the time in an aquarium. Can be done with some big assumptions. Assuming your aquarium water is pure water with pH 7 and also assuming that dissociation to H3PO4 and PO4 -3 is negligible (Kb of H2PO4- is 10^-12 and Ka of HPO4 2- is around 10^-13, we don't need to bother with them in the aquarium since the pH is never out of 5-8), adding 5e-5 M of phosphate in the form of KH2PO4 will result in a pH of 5.76
Of course the dissociation is less in an acidic solution, unfortunately CO2 and all the organic acids in our aquariums are weak acids so all the equilibriums will be pushing each other back and forth so it’s really hard to calculate. I might try later but I’m not too keen tbh lol.

Too many for me to bother with, good project if you are really interested in sum totals and lots of assumptions.

I'm just not that interested

Has little effect since I bypass KH/pH anyway for CO2 ppm's.

Regards,
Tom Barr

 

[Tom Barr]

The fact that I don't know the answer to this question sort of annoys me. Buffering questions pop up all the time and most people are just left shrugging. I'm downloading a textbook that should give some answers; it'll be done by tomorrow. I'm going to do my best to learn some of this, and perhaps write on the subject a little bit.

-Philosophos

Be careful, you may do lots of work that would be better spent on your tank/aquarium than muddling to some end point that applies only in some theoretical model with lots of assumptions.

If the question is really what is the CO2 ppm's, rather than the effect adding say 10ppm of PO4 as KH2PO4, then that's a very different question.

For most, aquarist simply want an adjustment to scale the KH up/down to account for higher PO4.

I think given all the other factor, that's fruitless, you can still wade through this if you wanna..............I think the main issue is really how to measure CO2, not KH really...........

Keep the goal in mind.
If it does not answer that, then the annoyances really matter little and you can let those go.



Regards,
Tom Barr

 

[Philosophos]

If it were just to play with carbonates for the sake of plants, I wouldn't do it. The fact is that I want a solid understanding of chemistry as it applies to the hobby. I've also got another passion in the hobby besides plants, but not exclusive to plants.

I find my self wanting to spawn apistos that require a pH around 5 for good responses and high viability. I'd like to do this with more precision than leaf litter; phosphoric acid comes to mind as an option. Until I have good command over my pH, I don't want to take on the more advanced species.

-Philosophos

 

[ordloh]

yeah tom you're right, too many assumptions. I'm actually really really bad at analytical chem i failed so hard for 1 minor test that it affected my 3 years of accumulated score lol. Philosophos, do you do it by solving simultaneous equations? I'm not really sure how it's suppose to be done XD
For a system with carbonate and phosphate, i had 9 unknowns : [H][H3PO4][H2PO4][HPO4][PO4][CO2][H2CO3][HCO3][CO3] but only 8 equations, 6 K equations, mass balance and charge balance. omg i hate this so much! and imagine if you have bits of calcium carbonate and iron phosphate in your substrate in equilbrium with your water

 

[charlie]

High PO4 influence on KH

The only reason for asking the question was for general knowledge, my curiosity was generated after reading this
"I truthfully do not know what levels of NO3 and PO4 (for example) cause problems for plants or induce algae in a fully planted tank. NO3 levels above 40ppm can cause fish health issues. PO4 at very high levels can influence alkalinity (KH) above 5ppm-10ppm." taken from Toms EI article.
http://www.barrreport.com/estimative-index/62-estimative-index-dosing-no-need-test-kits.html
I just wanted to know how the levels influence the alkalinity ?

 

[ordloh]

acidity/alkalinity in an aquarium is affected by the concentration of chemicals that release/absorb H+ respectively. eg strong acids like HCl (hydrochloric acid) dissociate completely to give H+ and Cl-, and because it dissociates completely we get a lot of H+. However Cl- never absorbs H+ to form HCl, so Cl- is not alkaline.
Weak acids like H2CO3(Carbonic acid) don't dissociate completely, they only release a fraction of the H+ attached to them into the water. CO3- is carbonate, or carbonic acid that has lost both its hydrogen. unlike Cl-, CO3- can absorb H+ from the water, hence CO3- is alkaline. Thats why adding calcium carbonate to the aquarium raises the pH. bicarbonate or HCO3- is carbonate that has only lost 1 hydrogen, and can either release or absorb hydrogen depending on the concentration of hydrogen around it.
similarly H2PO4- can either absorb or release H+ depending on the pH. in very acidic conditions, H2PO4- absorbs H to form H3PO4, hence it acts as a base. In more alkaline conditions, H2PO4- releases H+ and hence is an acid.

 

[Tom Barr]

If it were just to play with carbonates for the sake of plants, I wouldn't do it. The fact is that I want a solid understanding of chemistry as it applies to the hobby. I've also got another passion in the hobby besides plants, but not exclusive to plants.

I find my self wanting to spawn apistos that require a pH around 5 for good responses and high viability. I'd like to do this with more precision than leaf litter; phosphoric acid comes to mind as an option. Until I have good command over my pH, I don't want to take on the more advanced species.

-Philosophos

again, rather than organics, let's be even more specific.
Tannins, then take that another step farther, fluvic and humic acids.

What about those are beneficial to fish? Health? Disease? Pathogens? Metal toxicity(think about this one more as it pertains to tap waters etc).

Peat?
Soil base sediments and clays?

I'd think less and less about pH, more about having lower KH/rain water, lots of tannins. Easy to do with peat, which is what many who breed Apistos do.

That and excellent live food.

Regards,
Tom Barr

 

[Tom Barr]

yeah tom you're right, too many assumptions. I'm actually really really bad at analytical chem i failed so hard for 1 minor test that it affected my 3 years of accumulated score lol. Philosophos, do you do it by solving simultaneous equations? I'm not really sure how it's suppose to be done XD
For a system with carbonate and phosphate, i had 9 unknowns : [H][H3PO4][H2PO4][HPO4][PO4][CO2][H2CO3][HCO3][CO3] but only 8 equations, 6 K equations, mass balance and charge balance. omg i hate this so much! and imagine if you have bits of calcium carbonate and iron phosphate in your substrate in equilbrium with your water

When you add the organic acids, it'll get really nasty.
Borate, hydroxidies(tap water) and a dozen others, many of these will not have much influence. Softening done by the tap water supplier etc.

Each aquarium will have some subtle difference, enough to mess things up pretty good I'd speculate.

Since the focus might be asking the 2 questions posed:

1. Measure of CO2

2.Apisto breeding(peat + low KH tap/RO etc+ good live foods, more water changes)

Best not to use a method that makes it hard to answer either

Regards,
Tom Barr

 

[Philosophos]

Ordloh, I'm pretty lost on the whole thing, too. I didn't think it'd be this much of a headache.

Tom, do you know any reliable way to modify pH to a reasonable level with any loose consistency? I don't find peat shoveling to be my thing; I've sworn it off since the last batch of stuffed old pantyhose in a HOB.

-Philosophos

 

[Tom Barr]

I would not dismiss peat.
You can make extract and add that if that makes you feel better.

Another method is using Primfix?
Indian tea leaf extract etc.

Will not lower KH/pH, but may offer similar properties as tannins.

I measured CO2 indirectly with low KH/Peat/tannin laden water:

I used large water changes to make sure my KH/pH was a known level, and then set the CO2.

Then you keep the rate of CO2 delivery the same and reduce/drop the pH/KH/add tannins etc.

Since the rate of CO2 is the same, the ppm's should be very close to the same before and after you manipulate the pH/KH.

Regards,
Tom Barr

 

[Philosophos]

I've used peat before, and the most I can get without using a peat bottom is a drop from about 7.8 down to 7.2-4 from tap water. The mess just isn't worth the results if there are other ways. Peat bottoms in a small apartment make for an interesting mess, so I'm trying to avoid it.

So what is the purpose of tannins if not for the tannic acids? I thought the entire purpose was to drop out the KH/pH.

I like your CO2 rebounding idea; I was thinking on incorporating CO2, but never thought of it functioning that way along side the acids.

Have you done much for apisto spawning in the past?

-Philosophos