Using pH to Control Dosing of Bicarbonate vs Carbonate

Users Who Are Viewing This Thread (Total: 1, Members: 0, Guests: 1)

Dr. Jim

Valuable Member
View Badges
Joined
Nov 30, 2019
Messages
1,343
Reaction score
1,085
Location
Naples, FL
Rating - 0%
0   0   0
Before going ahead with my plan, I'd like to present it here to see if anyone sees any obvious flaws in my design or reasoning.

I'd like to dose Carbonate when the pH drops below 8.2 and Bicarbonate when it is equal to, or greater than 8.2. (Actually, the Bicarbonate will contain a small amount of Carbonate to avoid the temporary pH drop that occurs when dosing 100% Bicarbonate. This ratio is about 1 : 4.1 (Carb:Bicarb) when the pH is at 8.2 (verified by @JimWelsh). So there will be two reservoirs, one for Carb. and one for Bicarb., each controlled by separate dosers.
EDIT: @Randy Holmes-Farley just informed me that the initial pH drop from bicarbonate is only about 0.06 for an addition of 1.4 dKH, so this step is probably not essential.....(but I'm thinking, probably can't hurt either now that I know how to do it).

Since the dosing will be controlled by a (GHL) Timer (24 doses/day) the two solutions must yield equal dKH because the Controller function will only select which reservoir (Carb or Bicarb) that will be dosed, based on the pH. The same volume will be dosed because that amount is preset in the Timer so it is important that x mls of each buffer supplies the same amount of dKH.

For anyone interested in making the two solutions that will result in equal dKH, you would use 190.5 gm Soda Ash and fill to 1 gallon; and, 302 gm Bicarbonate and fill to 1 gallon. (also confirmed by Jim Welsh). (This relationship is also nice to know even if you just want to use one reservoir, and not the system I am describing. You could pour unequal amounts into the one reservoir without altering the dKH yield.....e.g. if your pH is lower than you want, you could just pour a random amount of carbonate in the reservoir without having to worry about altering the dKH dosage.)

I will begin by randomly selecting the nominal value of pH-1 = 8.2. Programable Logic would be used as follows:

P.L.-1 "AND" Function with Inputs 1 (Timer-1) and Input 2 (pH Downward) and would control Doser #1 (Carbonate). (Note: I have to review this and make sure it shouldn't be "pH Upward". When the pH DROPS to 8.2, I want this Doser #1 to activate.)

P.L. 2 "AND" Function with Inputs 1 (Timer-1) and Input 2 (pH Downward-INVERTED) and control Doser #2 (Bicarbonate). (This hasn't been tested yet so, again, I have to check and make sure these are the correct settings).

I'm choosing to use {"pH Downward" and "pH Downward-INVERTED"} instead of {"pH Downward" and "pH Upward"} because I think this will avoid the hysteresis interference that I would get if I used the latter. (I believe there would be no reaction at all over a narrow range around pH 8.2 if I set it up that way).

So, does any body see any problem with:
1)
The concept of using Carbonate when the pH is "low" and Bicarbonate when it is "not low"? The outcome will most likely be less of a daily pH swing. I guess the big question is, "Is there any benefit to that?"
2) The actual programming that I described?

Thanks for any ideas.
Jim
 
Last edited:

Brew12

Electrical Gru
View Badges
Joined
Aug 14, 2016
Messages
22,488
Reaction score
61,020
Location
Decatur, AL
Rating - 0%
0   0   0
Before going ahead with my plan, I'd like to present it here to see if anyone sees any obvious flaws in my design or reasoning.

I'd like to dose Carbonate when the pH drops below 8.2 and Bicarbonate when it is equal to, or greater than 8.2. (Actually, the Bicarbonate will contain a small amount of Carbonate to avoid the temporary pH drop that occurs when dosing 100% Bicarbonate. This ratio is about 1 : 4.1 (Carb:Bicarb) when the pH is at 8.2 (verified by @JimWelsh). So there will be two reservoirs, one for Carb. and one for Bicarb., each controlled by separate dosers.
EDIT: @Randy Holmes-Farley just informed me that the initial pH drop from bicarbonate is only about 0.06 for an addition of 1.4 dKH, so this step is probably not essential.....(but I'm thinking, probably can't hurt either now that I know how to do it).

Since the dosing will be controlled by a (GHL) Timer (24 doses/day) the two solutions must yield equal dKH because the Controller function will only select which reservoir (Carb or Bicarb) that will be dosed, based on the pH. The same volume will be dosed because that amount is preset in the Timer so it is important that x mls of each buffer supplies the same amount of dKH.

For anyone interested in making the two solutions that will result in equal dKH, you would use 190.5 gm Soda Ash and fill to 1 gallon; and, 302 gm Bicarbonate and fill to 1 gallon. (also confirmed by Jim Welsh). (This relationship is also nice to know even if you just want to use one reservoir, and not the system I am describing. You could pour unequal amounts into the one reservoir without altering the dKH yield.....e.g. if your pH is lower than you want, you could just pour a random amount of carbonate in the reservoir without having to worry about altering the dKH dosage.)

I will begin by randomly selecting the nominal value of pH-1 = 8.2. Programable Logic would be used as follows:

P.L.-1 "AND" Function with Inputs 1 (Timer-1) and Input 2 (pH Downward) and would control Doser #1 (Carbonate). (Note: I have to review this and make sure it shouldn't be "pH Upward". When the pH DROPS to 8.2, I want this Doser #1 to activate.)

P.L. 2 "AND" Function with Inputs 1 (Timer-1) and Input 2 (pH Downward-INVERTED) and control Doser #2 (Bicarbonate). (This hasn't been tested yet so, again, I have to check and make sure these are the correct settings).

I'm choosing to use {"pH Downward" and "pH Downward-INVERTED"} instead of {"pH Downward" and "pH Upward"} because I think this will avoid the hysteresis interference that I would get if I used the latter. (I believe there would be no reaction at all over a narrow range around pH 8.2 if I set it up that way).

So, does any body see any problem with:
1)
The concept of using Carbonate when the pH is "low" and Bicarbonate when it is "not low"? The outcome will most likely be less of a daily pH swing. I guess the big question is, "Is there any benefit to that?"
2) The actual programming that I described?

Thanks for any ideas.
Jim
I'm just seeing it and I love the detailed thinking!

The only issue I see with it is that you may not see much change in your pH graph even if this works exactly as designed. I suspect that the change in CO2 in the water will still be the dominant driver of pH through the days cycle unless you have extremely high alk demand in a small water volume. You would probably have better luck with pH control if you could use solenoid valves to select outside air or inside air on your skimmer intake.

That said, I see no harm in what you are doing and would love to see how it goes!
 
OP
OP
Dr. Jim

Dr. Jim

Valuable Member
View Badges
Joined
Nov 30, 2019
Messages
1,343
Reaction score
1,085
Location
Naples, FL
Rating - 0%
0   0   0
I'm just seeing it and I love the detailed thinking!

The only issue I see with it is that you may not see much change in your pH graph even if this works exactly as designed. I suspect that the change in CO2 in the water will still be the dominant driver of pH through the days cycle unless you have extremely high alk demand in a small water volume. You would probably have better luck with pH control if you could use solenoid valves to select outside air or inside air on your skimmer intake.

That said, I see no harm in what you are doing and would love to see how it goes!
I'm not real sure if I understand what you are saying. Sorry. Using the solenoid for inside air vs outside air is really the same thing as I am doing as I see it, except my pH range will be a notch higher by using outside air vs outside air scrubbed.
 

Brew12

Electrical Gru
View Badges
Joined
Aug 14, 2016
Messages
22,488
Reaction score
61,020
Location
Decatur, AL
Rating - 0%
0   0   0
I'm not real sure if I understand what you are saying. Sorry. Using the solenoid for inside air vs outside air is really the same thing as I am doing as I see it, except my pH range will be a notch higher by using outside air vs outside air scrubbed.
I don't see anything about using air in your post. Just selecting which alkalinity component is dosed.
 
OP
OP
Dr. Jim

Dr. Jim

Valuable Member
View Badges
Joined
Nov 30, 2019
Messages
1,343
Reaction score
1,085
Location
Naples, FL
Rating - 0%
0   0   0
I don't see anything about using air in your post. Just selecting which alkalinity component is dosed.
Oh sorry. Thought I was on a different thread! (I just woke up :) )
There is a thread where I talked about using a motorized ball valve to select "outside air" vs "outside air scrubbed."

But back to this thread.....yes I agree with you, the air is the dominant driver (which is why I am doing what I mentioned above with the "air control" . Right or wrong, a lot of what I do may because it may sound good in theory and I like to experiment and see what I can do with my GHL Controller (as long as I am confident it won't cause any harm).

My pH is pretty steady between 8.2 and 8.4 with a combination of these two methods.
 
Last edited:

Brew12

Electrical Gru
View Badges
Joined
Aug 14, 2016
Messages
22,488
Reaction score
61,020
Location
Decatur, AL
Rating - 0%
0   0   0
Oh sorry. Thought I was on a different thread! (I just woke up :) )
There is a thread where I talked about using a motorized ball valve to select "outside air" vs "outside air scrubbed."

But back to this thread.....yes I agree with you, the air is the dominant driver (which is why I am doing what I mentioned above with the "air control" . Right or wrong, a lot of what I do may because it may sound good in theory and I like to experiment and see what I can do with my GHL Controller (as long as I am confident it won't cause any harm).
(I wrote up the "programming" for this on the GHL forum).

My pH is pretty steady between 8.2 and 8.4 with a combination of these two methods.
Not a problem! Some days I forget my own personal rule about not posting before the first cup of coffee. ;)

I'll check that thread out, although I can't say I worry about pH stability too much.

My pH is typically between 8.1 and 8.3 without any control methods other than a reverse lit refugium. Mind my asking what your swings were?
 
OP
OP
Dr. Jim

Dr. Jim

Valuable Member
View Badges
Joined
Nov 30, 2019
Messages
1,343
Reaction score
1,085
Location
Naples, FL
Rating - 0%
0   0   0
I've got a lot of issues going on now....(see my "White Tips" thread in the SPS Forum), which is causing some alterations...but typically 8.2-8.4.

The programming I mentioned is actually in this thread....sorry! (I'm going back and forth between 3 threads too quickly at the moment which threw me off!)
 
Back
Top