Raising Carbonates without raising PH

[Richard Kowalski]

Hello,

I am just starting my flood and drain system. My system cycled, and I added some gold fish to start with. My PH was 6.8. Ammonia 0, Nitrites 0, Nitrates 40, KH 0.

I am amazed at how fast my plants are growing in the grow beds compared to my soil garden.

I added enough Potasium Bicarbonate to raise KH to 4. But now the PH is 8.

How do the experienced Aquapons keep the PH and Carbonates at an acceptable level without raising your PH every time you adjust KH?

Thanks

Rich K

[Charles Sublette]

I believe that is due to the aeration being severe enough thus injecting just enough atmospheric carbon dioxide into the water to interact with the carbonate to create the bicarbonate, but this can be a slow process since it is entirely dependent on the concentration of atmospheric CO2 versus you water's CO2 concentration. Due to this limitation, it may not work the same way for everyone.

A better route would be to directly inject the carbon dioxide such as using yeast & sugar co2 reactor or using water which already has a significant amount of carbon dioxide injected into it (i.e., carbonated water or seltzer water) then stir it rather than agitating it.

Potassium carbonate is essentially just a step or so behind potassium bicarbonate. The main difference between the two is that there is less carbon dioxide saturation in potassium carbonate.

But then... when there is all this manipulation of potassium carbonate, then can not say it is potassium carbonate anymore.

The purpose for Potassium Carbonate is when the pH wants to be raised with very little added alkalinity, such as to be used in low alkalinity systems. When folk want to maintain a higher alkalinity, then use Potassium Bicarbonate. This is why the aquaponicsource store has the AquaUp pH Raising kit (which is carbonate) and the AquaBuffer (which is bicarbonate).  It seems folk think the "intention of use" is the same for both products, except each product have different purposes with some crossover.

Carbonate is used to raise the pH, which also subsequently raises alkalinity to a small degree. Bicarbonate is used to raise the alkalinity, which also subsequently raises pH except not as much as carbonate..

However, point remains... since both products are on the same speciation curve... it still would not be possible to raise carbonate alkalinity without significantly raising the pH, unless significant tedious manipulation is conducted, which is not a safe thing to do.

Scott Roberts said:

Vlad - the high pH you experience when using potassium CARBONATE is a temporary effect. If you had aerated the water, the carbonate-bicarbonate equilibrium would have established itself, and the pH would have dropped to a 7sometime number. 

The important thing is to stop using Potassium Carbonate. I can't recall one reference that says "use Potassium Carbonate".

[Charles Sublette]

That is due to the carbon dioxide the vinegar helped to create.

This thread might be interesting to you... TheKrib - CO2 and Alkalinity.

also... the bicarbonate pH equation is .... pH = pKa + log ( [ HCO3- ] / [ H2CO3 ] ) ... H2CO3 is dissolve carbon dioxide.

This is what I was talking about in forcing water with an alkalinity, such as 6 dKH, to being on the "low end of the pH swing" due to carbon dioxide.

The reason your water has a 6 dKH and pH around 7.2 is that you are forcing a "low end" pH swing due to the carbon dioxide contribution from the vinegar.

This is not a good thing because... think about what happens once the carbon dioxide is eventually released out of the water. It will eventually swing back up to near 8.2.

Carbon dioxide acts differently in water than other typical acids since carbonic acid is the weak acid companion of the bicarbonate/carbonate salt, which is what creates the buffer.

This is why carbon dioxide can lower pH with minimal impact on alkalinity.

Joe Fisher said:

Interesting topic. Thanks for all the info by posters in this thread!

I did a small sample test over the past 24 hours in a 5 gallon bucket with tap water. Which comes out here with a pH near 8.2.

So in this 1 5 gallon bucket I added 1/2 TBS of vinegar. Tested the pH it was around 7.2 this was last evening. Tested it again in the morning. Still around 7.2. Worked all day. Then came home and tested it again. Still around 7.2.

I then decided to test the kH. Interesting that kH ended up at near 6 dkH.

Just find it curious as to what vinegar does do to water. As this test doesn't seem to make sence.

Just adding this to the thread.

-Joe

[Alex Veidel]

[salute] Thank you Charles :D

Charles Sublette said:

I believe that is due to the aeration being severe enough thus injecting just enough atmospheric carbon dioxide into the water to interact with the carbonate to create the bicarbonate, but this can be a slow process since it is entirely dependent on the concentration of atmospheric CO2 versus you water's CO2 concentration. Due to this limitation, it may not work the same way for everyone.

A better route would be to directly inject the carbon dioxide such as using yeast & sugar co2 reactor or using water which already has a significant amount of carbon dioxide injected into it (i.e., carbonated water or seltzer water) then stir it rather than agitating it.

Potassium carbonate is essentially just a step or so behind potassium bicarbonate. The main difference between the two is that there is less carbon dioxide saturation in potassium carbonate.

But then... when there is all this manipulation of potassium carbonate, then can not say it is potassium carbonate anymore.

The purpose for Potassium Carbonate is when the pH wants to be raised with very little added alkalinity, such as to be used in low alkalinity systems. When folk want to maintain a higher alkalinity, then use Potassium Bicarbonate. This is why the aquaponicsource store has the AquaUp pH Raising kit (which is carbonate) and the AquaBuffer (which is bicarbonate).  It seems folk think the "intention of use" is the same for both products, except each product have different purposes with some crossover.

Carbonate is used to raise the pH, which also subsequently raises alkalinity to a small degree. Bicarbonate is used to raise the alkalinity, which also subsequently raises pH except not as much as carbonate..

However, point remains... since both products are on the same speciation curve... it still would not be possible to raise carbonate alkalinity without significantly raising the pH, unless significant tedious manipulation is conducted, which is not a safe thing to do.

[Joe Fisher]

Thanks Charles! I'll take a proper look at the link also when I get some time.

[Charles Sublette]

This is why I don't like acetic acid, that is vinegar, to lower the water's pH due to the creation of carbon dioxide and the acetate is also metabolized by microorganisms thus depletes some dissolved oxygen out of the water, but vinegar is cheap and sometimes can be effective at controlling pH, depending on the alkalinity.

The practice of using carbon dioxide so to have a lower water pH while maintaining a higher carbonate alkalinity is commonly practiced in the planted aquarium hobby.

However, this can be a dangerous practice when fish are involved since carbon dioxide essentially suffocates fish by preventing the fish's osmoregulatory system from properly functioning to release the carbon dioxide out of their body thus poisoning them self. If water's carbon dioxide concentration is too high, then the fish can not respire, that is release carbon dioxide, thus they eventually suffocate, or posion, them self.

This is how fish can die due to lack of oxygen while still in oxygen saturated water.

When circulating and agitating the water, we are more so releasing toxic gases, such as carbon dioxide respired by fish and algae and other organisms, rather than oxygenating the water, even though the water is also being oxygenated.

The impact of water stratification, water pH, and water alkalinity on carbon dioxide and how it relates to our context is quite interesting.

Joe Fisher said:

Thanks Charles! I'll take a proper look at the link also when I get some time.

[Charles Sublette]

Here is an eHow article on how to convert carbonate into bicarbonate while using vinegar as the carbon dioxide source. The same can be dome with Potassium Carbonate to convert it into Potassium Bicarbonate.

Remember what I wrote earlier, "Carbonate is used to raise the pH, which also subsequently raises alkalinity to a small degree, as referenced and verified by the aquaponicsource store product called AquaUp Raisking Kit. Bicarbonate is used to raise the alkalinity, which also subsequently raises pH except not as much as carbonate, as referenced and verified by the aquaponicsource store product called AquaBuffer."

Better to just buy Potassium Bicarbonate on its own if your only mission is to raise alkalinity, but, if you already have Potassium Carbonate on hand due to your need to occasionally raise the pH, then you can also easily, on your own, convert this into Potassium Bicarbonate.

You convert Potassium Carbonate into Potassium Bicarbonate by mixing carbon dioxide with Potassium Carbonate. You can use any carbon dioxide delivery mechanism such as carbonated water or vinegar or extreme aeration or yeast+sugar. Remember, do not significantly agitate it too much less you risk the chance of expelling the carbon dioxide before it can fully react properly with the Potassium Carbonate.

The reason severe aeration on its own can sometimes do the trick is explained in a couple posts back of mine.

Once it has finished reacting by observing the change in the pH to reach around 8.4~8.6, then follow the comment, at the bottom of the eHow instructions, on how to reduce the now newly created Potassium Bicarbonate liquid solution so to create the Potassium Bicarbonate powder.

I was doing some quick searching for good visual demonstrations to share on how to create your own carbon dioxide and found this very cute YouTube video, Fun Yeast Experiment to measure carbon dioxide output.

[Joe Fisher]

Thanks again Charles! Indeed interesting.

I also sent you a friend request.

[Charles Sublette]

The reason the pH would be in the "10.2 pH range with a dKH of 3 or 4" is due to the carbonate (CO32-), potassium carbonate.

If it was bicarbonate (HCO3-), that is potassium bicarbonate, then the 3~4 dKH would have a much lower pH.

This is why I was compelled in my post (jun10, 9:34pm) in this thread to clarify that i was talking about bicarbonate when I mentioned "carbonate" buffed water. In the koi/goldfish pond hobby, this clarification is not required since the two terms "carbonate" and "bicarbonate" are used interchangeably, but, in the aquaponic hobby context, these terms are often not used interchangeably, which is quite fine and a bad habit of mine carried over from the koi/goldfish hobby.

Scott Roberts said:

Vlad - why do you think pH will be in the 10.2 range with a dKH of3 or 4? 

Vlad Jovanovic said:

You framed the question perfectly Richard  I've been wondering the very same thing!

It is very unlikely (read impossible, as far as I can tell) to use your potassium carbonate and calcium carbonate to obtain a KH of dH3-4 while having anything resembling even a remotely sane pH. Your pH will be in the pH10.2 or so range if you do that.

[Charles Sublette]

I just noticed you lumped in calcium carbonate in there and I have to say that this is not entirely true for calcium carbonate, in crystal formation such as chicken grit or crushed oyster shells or aragonite etc, due to the low solubility since calcium has a very strong attraction to carbonate.

Potassium carbonate is far more soluble than calcium carbonate due to the weaker electrochemical bond between potassium and carbonate. This higher solubility is what causes the carbonate formation of potassium carbonate to increase the pH so effectively.

Calcium carbonate solubility is so low that it actually stops dissolving at around 8.6 pH and the dissolve rate is quite negligible when pH is at around 7.8 pH. This is why acid is required to dissolve it and this acid is often carbonic acid that converts this into bicarbonate.

Vlad Jovanovic said:

You framed the question perfectly Richard  I've been wondering the very same thing!

It is very unlikely (read impossible, as far as I can tell) to use your potassium carbonate and calcium carbonate to obtain a KH of dH3-4 while having anything resembling even a remotely sane pH. Your pH will be in the pH10.2 or so range if you do that.

The soluable carbonates are wonderful for raising pH, but offer about as much of a "buffer" as hydroxides do (very little).

You probably want to use potassium bicarbonate (not carbonate, but bicarbonate) to afford yourself any noticeable rise in KH (and not have to fiddle with pH daily). Though be aware that even then, you in all reality (or anything resembling it) likely will not be able to hold a KH of dH3-4, and be in the suggested pH range of 6.4 to 6.8 (as you and others have already noticed). With the bicarbonate you will be near pH8 at dH3-4.

The KH does seem to be very important during the cycling stages (when you are running a high pH and KH to allow the bacteria to become established), but beyond that I'd shoot for dH 0.5 or so.

I'm not sure how Steve R is able to hold a pH in the mid 6's and a dH of 3-4, but will be going to Colorado in a couple of months and will hopefully find out.

[Charles Sublette]

Bah, the edit timer is too quick.. .Quick correction on myself due to having to looking this up in my college chemistry textbook due to a bugging itch of mine wanting to be sure of what I type is correct as far as I know it.

Calcium carbonate solubility stops at around 8.2 pH in crystal formation.

In other words, it is impossible for calcium carbonate to increase the water's pH as high as potassium carbonate even though they are both a carbonate formation.

Solubility, thus the potential pH affect, is more about the electrochemical bond, which is why soda ash is used more often to be mixed in with baking soda for aquarium buffers due to sodium's very weak electrochemical bond with its counterpart.

Charles Sublette said:

Calcium carbonate solubility is so low that it actually stops dissolving at around 8.6 pH and the dissolve rate is quite negligible when pH is at around 7.8 pH. This is why acid is required to dissolve it and this acid is often carbonic acid that converts this into bicarbonate.

[Evergreen_AP]

Hello Vlad - I'm also trying to lean more about this, just a year+ removed from this conversation.  I was curious if your trip to CO shed any light or if you still believe your following statements?:

The KH does seem to be very important during the cycling stages (when you are running a high pH and KH to allow the bacteria to become established), but beyond that I'd shoot for dH 0.5 or so.

I'm not sure how Steve R is able to hold a pH in the mid 6's and a dH of 3-4, but will be going to Colorado in a couple of months and will hopefully find out.

Vlad Jovanovic said:

You framed the question perfectly Richard  I've been wondering the very same thing!

It is very unlikely (read impossible, as far as I can tell) to use your potassium carbonate and calcium carbonate to obtain a KH of dH3-4 while having anything resembling even a remotely sane pH. Your pH will be in the pH10.2 or so range if you do that.

The soluable carbonates are wonderful for raising pH, but offer about as much of a "buffer" as hydroxides do (very little).

You probably want to use potassium bicarbonate (not carbonate, but bicarbonate) to afford yourself any noticeable rise in KH (and not have to fiddle with pH daily). Though be aware that even then, you in all reality (or anything resembling it) likely will not be able to hold a KH of dH3-4, and be in the suggested pH range of 6.4 to 6.8 (as you and others have already noticed). With the bicarbonate you will be near pH8 at dH3-4.

The KH does seem to be very important during the cycling stages (when you are running a high pH and KH to allow the bacteria to become established), but beyond that I'd shoot for dH 0.5 or so.

I'm not sure how Steve R is able to hold a pH in the mid 6's and a dH of 3-4, but will be going to Colorado in a couple of months and will hopefully find out.

[Alex Veidel]

Also curious about this.

And a follow up question: Do carbonates hold water at a specific pH value or do they simply resist changes in pH?

I've been batting around the idea of running a low pH, while still maintaining enough kH for crustaceans like prawns or crayfish. I'm curious if I could drop the pH of my water lower than my target pH in a seperate barrel and then add in the carbonates afterwards to bring it back up to my desired range.