Equation for graphing Alk vs pH for a given CO2 level

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@Randy Holmes-Farley Could you share the equation(s) used for making this graph?
figure2-da3879f93b396574f9a20bd27585297d.gif
 
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Randy Holmes-Farley

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Yes, but its not a simple equation and some approximations are needed.

Here' it is in all its glory:


See section 2.2.1, fourth equation down.

I did it a long time ago, but I think I also assumed that Ct scales linearly with CO2 and that the CO2 in the water scales linearly with CO2 in the air (that last part is true at equilibrium).
 

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Check this thread for a generated table of alk, pH, CO2.
Slightly less intimidating than the equation. :)
 
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Yes, but its not a simple equation and some approximations are needed.

Here' it is in all its glory:


See section 2.2.1, fourth equation down.

I did it a long time ago, but I think I also assumed that Ct scales linearly with CO2 and that the CO2 in the water scales linearly with CO2 in the air (that last part is true at equilibrium).

That might be a little too complex for me to suss out the equations and related graphs.

Check this thread for a generated table of alk, pH, CO2.
Slightly less intimidating than the equation. :)

This is exactly what I was looking to generate! Is the table data verified?
 

taricha

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This is exactly what I was looking to generate! Is the table data verified?
You'll find it agrees pretty well with Randy's posted plot.

from table (NBS scale) at 700ppm pCO2
pH -- dKH -- meq/L
8.0 -- 6.6 -- 2.4
8.1
-- 8.6 -- 3.1
8.2
-- 11.3 -- 4.1

compare the bold pH vs meq/L to the red line on the plot above.
 
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The reason I'm looking into this is that everyone in the hobby says stability is key. However, day/night pH swings are considered fine but should just be minimized. There isn't a lot of fucos in this area and many hobbiest don't even bother with it.

There is a huge focus on Alk/Ca stability and equipment to regulate this.

I'm in the camp of slightly elevated NSW parameters levels as best for reefing success.

My pH was typically swinging between 7.8 - 7.9. In my journey to get that slightly elevated, I ended up being able to lock the pH in day and night +/- .025, but more typically +/- 0.01.

The question I am now asking is if this is even beneficial and how locking in pH effects other parameters.

This led to Randy's articles about pH/CO2/Alk.

With locked in pH, as my Alk rises and falls, my CO2 levels falls and rises.

With my pH of 8.3 (whether it's measured correctly or not) I should be targeting a dKH of 7.6 to maintain normal 350ppm CO2 levels. If I raise my Alk higher, I'm essentially raising the tanks CO2 levels. If I go lower with Alk, I'm essentially lowering CO2 levels below NSW.

I know many reefers with a pH of 8, drive their Alk to 11. This essentially is driving up CO2 levels. Are they better off at a lower Alk?

The most successful reefers I've come across locally keep their Alk in the mid 7s.
 
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I sort of want to put together your tank's chemical journey focussed on the following parameters (Temp, Salinity, pH, Alk, Ca, NO3, PO4, major/minor ions) and achieving stability. I'll probably just focus on pH, Alk, Ca, as it probably too big to bite off.

1. Fresh ASW --> NSW parameters
2. Aerated ASW --> usually drops pH
3. Adding substrate (CaCO3 source) --> lower pH allows CaCO3 substrate to contribute Alk/Ca
4. Bacteria + Ammonia --> ammonia to NO3 consumes a small amount of Alk
5. Adding fish and food --> will produce NO3 and PO4
6. Lighting and algae growing -> NO3 and PO4 w/ light produces algae along with other organisms lead to day/night pH swings --> pH swings contribute to Alk consumption swings
7. Coraline algae and coral --> Increased demand for Alk/Ca/NO3/PO4/Bacteria
8. Eventual CaCO3 surface poisoning from PO4 and Magnesium --> reduced abiotic precipitation and/or disassociation
9. Seasoned Tank
 

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The question I am now asking is if this is even beneficial and how locking in pH effects other parameters.

I agree it is an unanswered question, partly because it is harder to control than alk or calcium.

It is the basis for this recent thread of mine:

 
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I agree it is an unanswered question, partly because it is harder to control than alk or calcium.

It is the basis for this recent thread of mine:


@Randy Holmes-Farley I'll read through the thread. As I've chased pH and achieved stability, I'm focused on Alk stability next. I'm targeting 7.6ish. If I switch away from AFR to two-part, I can use my GHL to more easily lock in Alk. I did this when I was doing the Triton method.

Would there be some valuable data I could contribute?
 

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@Randy Holmes-Farley I'll read through the thread. As I've chased pH and achieved stability, I'm focused on Alk stability next. I'm targeting 7.6ish. If I switch away from AFR to two-part, I can use my GHL to more easily lock in Alk. I did this when I was doing the Triton method.

Would there be some valuable data I could contribute?

1. Does a stable pH at a fixed alk promote coral growth/health/appearance? Or hurt it?

2. Really interesting to me: if pH is stable, is the alk consumption as focused during the daytime as most folks now report? What if the tank is actually pH reversed, with lower pH during the day. Is the alk still consumed mostly/only during the day?
 
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1. Does a stable pH at a fixed alk promote coral growth/health/appearance? Or hurt it?

2. Really interesting to me: if pH is stable, is the alk consumption as focused during the daytime as most folks now report? What if the tank is actually pH reversed, with lower pH during the day. Is the alk still consumed mostly/only during the day?

So I'm not sure I would be able to answer #1. Despite several weeks of very fixed pH, my coral successes has been pretty low. I believe that nutrients, light, and flow still need more work in my tank. I added a Copper Banded Butterfly last week and started overfeeding my tank...my Jellybean Chalice is now growing like crazy. Everything else, not so much.

With regard to #2, I can say I saw no difference in day/night Alk consumption. Then again, it's still a very lightly stocked and new tank.

Last week I also bought some algae barn snake oil (Coraline Algae in a bottle) to see if I can get that growing in the tank. The small rocks and stuff brought from old tank have it, but it hasn't spread.

Reversing day/night pH could easily be achieved...but again I see no day/night alk differences.
 

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So I'm not sure I would be able to answer #1. Despite several weeks of very fixed pH, my coral successes has been pretty low. I believe that nutrients, light, and flow still need more work in my tank. I added a Copper Banded Butterfly last week and started overfeeding my tank...my Jellybean Chalice is now growing like crazy. Everything else, not so much.

With regard to #2, I can say I saw no difference in day/night Alk consumption. Then again, it's still a very lightly stocked and new tank.

Last week I also bought some algae barn snake oil (Coraline Algae in a bottle) to see if I can get that growing in the tank. The small rocks and stuff brought from old tank have it, but it hasn't spread.

Reversing day/night pH could easily be achieved...but again I see no day/night alk differences.

It's a hard experiment to do. :)
 

taricha

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My pH was typically swinging between 7.8 - 7.9. In my journey to get that slightly elevated, I ended up being able to lock the pH in day and night +/- .025, but more typically +/- 0.01.

The question I am now asking is if this is even beneficial and how locking in pH effects other parameters.

This led to Randy's articles about pH/CO2/Alk.

With locked in pH, as my Alk rises and falls, my CO2 levels falls and rises.

With my pH of 8.3 (whether it's measured correctly or not) I should be targeting a dKH of 7.6 to maintain normal 350ppm CO2 levels. If I raise my Alk higher, I'm essentially raising the tanks CO2 levels. If I go lower with Alk, I'm essentially lowering CO2 levels below NSW.
This confuses me (though I understand how the math of Alk/pH/CO2 predicts the relationship).
How are you locking in pH in a way that if you run alk higher it pushes CO2 up?
What are your mechanisms for controlling super-stable pH?
 
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This confuses me (though I understand how the math of Alk/pH/CO2 predicts the relationship).
How are you locking in pH in a way that if you run alk higher it pushes CO2 up?
What are your mechanisms for controlling super-stable pH?

Here is todays's pH...

1620332993356.png
 

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