Can kalk dosing rate influence pH impact?

[rishma]

My question:
For the same total Kalk volume, is it plausible that varying the hourly kalkwasser dose rate during the dark period can increase the average pH during the daylight period as compared to a constant dosing rate during the dark period?

For example, all other things being equal could dosing at a higher rate during the hours Immediately after lights go out and a lower rate for the ours immediately before the before lights come on result in higher overall pH during the day? (Or the complete opposite dosing pattern). The base case being using the same dosing rate every hour the lights are out and the same total Kalkwasser volume.

A few of givens:
Using the same kalk dose per 24 hours. For my 100L tank I’ll use 200ml kalk.

Maintainkng the same average alkalinity, shooting for 8.8-9 dKH.

I am assuming higher pH during the daylight hours is a good thing.

Context:
I dose saturated kalkwasser at night to supplement Ca/Alk and mitigate the pH swing. For a very long time, I have dosed a constant rate during the hours the lights are off.

I am wondering if there is a basis for achieving higher overall pH boost by varying the dosing rate. Without sharing my (potentially wrong) rationale, I am wondering if changing CO2 concentrations in the water at night and potential time dependent reactions between Kalk and CO2 (and pH) could be influenced with Kalk dosing rate. I expect thermodynamically its equivalent.

I could do an experiment sometime in the next couple of weeks, but I figured I’d ask for some feedback on the idea before doing it.

Thanks in advance for your thoughts.

 

[Randy Holmes-Farley Verified Community Expert]

Two points based on one principle: adding hydroxide creates a deficit of CO2 in the water relative to the air, and that deficit draws in CO2 at a rate related to the difference in CO2 concentration.

1. The closer in time to daytime the deficit occurs, the less time for CO2 to be drawn in, and the higher the daytime pH will be.

2. A large spike in CO2 deficit from a large dose in the early part of the night will be dissipated more by morning than would a bunch of smaller spikes to the same total dose, with the last spike close to daytime.

 

[Garf]

My question:
For the same total Kalk volume, is it plausible that varying the hourly kalkwasser dose rate during the dark period can increase the average pH during the daylight period as compared to a constant dosing rate during the dark period?

For example, all other things being equal could dosing at a higher rate during the hours Immediately after lights go out and a lower rate for the ours immediately before the before lights come on result in higher overall pH during the day? (Or the complete opposite dosing pattern). The base case being using the same dosing rate every hour the lights are out and the same total Kalkwasser volume.

A few of givens:
Using the same kalk dose per 24 hours. For my 100L tank I’ll use 200ml kalk.

Maintainkng the same average alkalinity, shooting for 8.8-9 dKH.

I am assuming higher pH during the daylight hours is a good thing.

Context:
I dose saturated kalkwasser at night to supplement Ca/Alk and mitigate the pH swing. For a very long time, I have dosed a constant rate during the hours the lights are off.

I am wondering if there is a basis for achieving higher overall pH boost by varying the dosing rate. Without sharing my (potentially wrong) rationale, I am wondering if changing CO2 concentrations in the water at night and potential time dependent reactions between Kalk and CO2 (and pH) could be influenced with Kalk dosing rate. I expect thermodynamically its equivalent.

I could do an experiment sometime in the next couple of weeks, but I figured I’d ask for some feedback on the idea before doing it.

Thanks in advance for your thoughts.

I think it averages out. Dose it at night and higher pH when the lights come on. Dose it 24 hrs and lower at night but higher during the day. Dose during the day and lower when the lights come on, but higher at the end of the photoperiod. I wouldn't expect much of a rise with 200ml in a 100 litre tank to be honest. How far away from pH 8.2/3 are you?

 

[rishma]

Two points based on one principle: adding hydroxide creates a deficit of CO2 in the water relative to the air, and that deficit draws in CO2 at a rate related to the difference in CO2 concentration.

1. The closer in time to daytime the deficit occurs, the less time for CO2 to be drawn in, and the higher the daytime pH will be.

2. A large spike in CO2 deficit from a large dose in the early part of the night will be dissipated more by morning than would a bunch of smaller spikes to the same total dose, with the last spike close to daytime.

Thanks. This helps. I may experiment ramping up dose rate through the night or dosing at a higher rate the last few hours. I wonder how long the hydroxide-CO2 reaction takes (mixing, etc) vs how long it takes CO2 to be drawn in. If the hydroxide reaction is fast compared to the CO2 coming into the water, maybe it’s possible I can carry a CO2 deficit into the photoperiod and achieve higher pH.

Thinking further, the pH drop at night it not linear. The rate of change is much higher in the first few hours of dark than in the last few hours. Maybe this is because the water is CO2 deficient at the end of the photoperiod and the concentration of CO2 at the end of the night period is closer equilibrium with the air so the rate of being dissolved in the water is slower toward the morning. Or is it because the CO2 pH relationship is not linear?

 

[Randy Holmes-Farley Verified Community Expert]

Thanks. This helps. I may experiment ramping up dose rate through the night or dosing at a higher rate the last few hours. I wonder how long the hydroxide-CO2 reaction takes (mixing, etc) vs how long it takes CO2 to be drawn in. If the hydroxide reaction is fast compared to the CO2 coming into the water, maybe it’s possible I can carry a CO2 deficit into the photoperiod and achieve higher pH.

Thinking further, the pH drop at night it not linear. The rate of change is much higher in the first few hours of dark than in the last few hours. Maybe this is because the water is CO2 deficient at the end of the photoperiod and the concentration of CO2 at the end of the night period is closer equilibrium with the air so the rate of being dissolved in the water is slower toward the morning. Or is it because the CO2 pH relationship is not linear?

The effect of CO2 on pH is not linear (it’s greater at lower pH) and the effect in a tank is very complicated since CO2 can come from organisms and also can come or go from the tank to the air.

 

[rishma]

Here’s some more details:

The effect of CO2 on pH is not linear (it’s greater at lower pH) and the effect in a tank is very complicated since CO2 can come from organisms and also can come or go from the tank to the air.

CO2has a greater impact at lower pH? Ok!

I suppose that means the slower rate of pH decline towards the end of the night might be due to the CO2 in the water approaching equilibrium with the air. There is more CO2 in the water at that time but less CO2 is added to the water in the last hour as compared to the first hour.

Does that sound right to you?

 

[rishma]

I think it averages out. Dose it at night and higher pH when the lights come on. Dose it 24 hrs and lower at night but higher during the day. Dose during the day and lower when the lights come on, but higher at the end of the photoperiod. I wouldn't expect much of a rise with 200ml in a 100 litre tank to be honest. How far away from pH 8.2/3 are you?

Your argument is good, but I’m not convinced it’s true for my tank. I could definitely be wrong!! Note: I should have been clear I do not have a pH problem I am trying to solve, I am just tinkering. Here is my thinking:

I aerate my tank with outside air. This means I have less excess CO2 in the tank now than I used to. pH is higher as a result. My pH is 8.2-8.4 averaging 8.3. it’s lower recently by a few tenths due to lower light intensity. It does vary some based on a number of factors, but that’s about typical.

When the lights are on photosynthesis does a great job of consuming CO2. I am assuming the photosynthesis has a bigger impact than my Kalk because, As you stated, it’s not a large dose.

If I can optimize the hydroxide reacting with the CO2 coming in at night, I am thinking I could reduce the average amount of CO2 and therefore raise the average pH. This might all be bunk, but it’s fun to think about :)

 

[Garf]

My pH is 8.2-8.4 averaging 8.3

Fab :)

 

[Randy Holmes-Farley Verified Community Expert]

Here’s some more details:

CO2has a greater impact at lower pH? Ok!

I suppose that means the slower rate of pH decline towards the end of the night might be due to the CO2 in the water approaching equilibrium with the air. There is more CO2 in the water at that time but less CO2 is added to the water in the last hour as compared to the first hour.

Does that sound right to you?

Yes, that would be my expectation.

 

[bobnicaragua]

Your argument is good, but I’m not convinced it’s true for my tank. I could definitely be wrong!! Note: I should have been clear I do not have a pH problem I am trying to solve, I am just tinkering. Here is my thinking:

I aerate my tank with outside air. This means I have less excess CO2 in the tank now than I used to. pH is higher as a result. My pH is 8.2-8.4 averaging 8.3. it’s lower recently by a few tenths due to lower light intensity. It does vary some based on a number of factors, but that’s about typical.

When the lights are on photosynthesis does a great job of consuming CO2. I am assuming the photosynthesis has a bigger impact than my Kalk because, As you stated, it’s not a large dose.

If I can optimize the hydroxide reacting with the CO2 coming in at night, I am thinking I could reduce the average amount of CO2 and therefore raise the average pH. This might all be bunk, but it’s fun to think about :)

Did you switch to dosing kalk at night and what was the result?

 

[rishma]

Did you switch to dosing kalk at night and what was the result?

I’ve dosed kalkwasser at night for the better part of 30 years :). the result has always been a smaller pH drop overnight.

My original question was whether manipulating the hourly rate of kalkwasser could enhance the pH effect.

I have not gotten around to completing this experiment because I ended up going a different route, combating CO2 with aeration.

 

[bobnicaragua]

I’ve dosed kalkwasser at night for the better part of 30 years :). the result has always been a smaller pH drop overnight.

My original question was whether manipulating the hourly rate of kalkwasser could enhance the pH effect.

I have not gotten around to completing this experiment because I ended up going a different route, combating CO2 with aeration.

Gotcha, I was stubborn for years and just dosed kalk continuously. When I switched to dosing the same daily amount overnight, my tank took off.

 

[Pod_01]

I’ve dosed kalkwasser at night for the better part of 30 years :). the result has always been a smaller pH drop overnight.

Hmmm, and after 30 years no broken buffer system or old tank syndrome, interesting…

On a serious note, do you use Kalk at night and something else during the day?
I am planning to experiment with soda ash again and am debating if I should equal dose or dose more at night etc…
I like to keep things simple so equal dosing may be the way. But this discussion is interesting and I may experiment some more.

 

[rishma]

Hmmm, and after 30 years no broken buffer system or old tank syndrome, interesting…

On a serious note, do you use Kalk at night and something else during the day?
I am planning to experiment with soda ash again and am debating if I should equal dose or dose more at night etc…
I like to keep things simple so equal dosing may be the way. But this discussion is interesting and I may experiment some more.

To be fair, 30 years and multiple different tanks.

I dose AFR at beginning of light cycle.

For a while I tested alkalinity morning and evening to see the swing and it was pretty small, maybe 0.2 dKH change but I’m sure that will vary with alkalinity demand.

 

[sayurasem]

I am thinking about this as well, but backwards. The idea is to carry the CO2 deficit from photoperiod and keep it through the night. At the end of the day CO2 equilibrium sucks.

 

[rishma]

I am thinking about this as well, but backwards. The idea is to carry the CO2 deficit from photoperiod and keep it through the night. At the end of the day CO2 equilibrium sucks.

I was running a higher dose rate of Kalk early in the night with a lower dose rate toward the morning. Today I switched it so tonight I’ll run a lower dose rate right after lights out and ramp up to a higher dose rate is in morning. I’ll report back if I notice anything different.