Mixing BRS Soda Ash and Sodium Bicarbonate

[Ippyroy]

I have a great naturally high PH of around 8.26. When I dose Soda Ash it will rise to a little over 8.4. I also live in an extremely cold location. 47 below zero is rather common. This winter I will be sealing the windows in an effort to stop the temp swings inside. This will increase the CO2 and therefore lower my PH. I am considering trying to mix both Soda Ash and Sodium Bicarbonate to limit the increase in PH. My problem is what ratio and how much would I dose? For each percentage of SB do I also increase the dosage? IE if I mix 1/3 SB to 2/3 SA, do I dose 1/3 more and go from there?

 

[Anchor]

Following this one.. I dont have an answer for you.. but it is a great question, something I can use... Maybe there is someone we can @ xxxx

 

[Randy Holmes-Farley Verified Community Expert]

You can mix any ratio you want (although normallly one or the other is fine), but bicarbonate is less soluble than carbonate, which is why my two dosing solutions have different potency.

If you make the two solutions and combine them 1:1, the potency is exactly the average of the two:

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System by Randy Holmes-Farley - Reefkeeping.com

 

[jdog6973]

So I have been using 2 cups of BRS sodium bicarbonate and 1 tablespoon of BRS soda ash for years because if I use straight soda ash my ph goes through the roof.

 

[Randy Holmes-Farley Verified Community Expert]

So I have been using 2 cups of BRS sodium bicarbonate and 1 tablespoon of BRS soda ash for years because if I use straight soda ash my ph goes through the roof.

IMO, I'd use more sodium carbonate because your pH is on the low side.

 

[Dr. Jim]

@Randy Holmes-Farley
If you dilute your DIY Bicarbonate solution in half (so it yields 2660 dKH) then would it be true that you could then mix the bicarbonate and carbonate solutions in any ratio and still have the combination yield the same dKH? I'm thinking that this might be helpful. If we want a higher pH we could just pour some extra carbonate in the dosing reservoir (or bottle) without needing to know the volume in the container or performing calculations and it would have no affect on the amount of dKH that we are dosing.

Also, how important is it to dry the baking soda or soda ash before use? And should the weight measurements be made before or after the drying?

One more question related to drying: I recently dried Morton salt (for the DIY salinity calibration solution) at 350F for 25 min and the salt turned a slightly brown color which caused the solution to have a slightly brown tint. Do you think this solution is OK to use?

Thank you.

 

[Randy Holmes-Farley Verified Community Expert]

@Randy Holmes-Farley
If you dilute your DIY Bicarbonate solution in half (so it yields 2660 dKH) then would it be true that you could then mix the bicarbonate and carbonate solutions in any ratio and still have the combination yield the same dKH?

You mean dilute the carbonate one by half? if so, yes.

@Randy Holmes-Farley

Also, how important is it to dry the baking soda or soda ash before use? And should the weight measurements be made before or after the drying?

Not important. Weigh them as is.

One more question related to drying: I recently dried Morton salt (for the DIY salinity calibration solution) at 350F for 25 min and the salt turned a slightly brown color which caused the solution to have a slightly brown tint. Do you think this solution is OK to use?

Hmm. Should be OK. What browned was the organic in it (dextrose, last I checked). It shouldn't alter the refractive index noticeably.

 

[jdog6973]

IMO, I'd use more sodium carbonate because your pH is on the low side.

I have always tried to use your Table as a reference.
So would you aim to be closer to 8.3?

 

[Dr. Jim]

Dr. Jim said:
@Randy Holmes-Farley

Also, how important is it to dry the baking soda or soda ash before use? And should the weight measurements be made before or after the drying?

Not important. Weigh them as is.

Randy, I was thinking that the weight would be different after baking.

What I am trying to do is make a solution of carbonate and a solution of bicarbonate where they both yield the same dKH. For now, I want to use up some BRS soda ash but was not able to find in your articles how many grams to use in any particular formula. In your "Improved DIY 2-Part...." article, for recipe #1 you dry 594 gm bicarbonate (presumably to make carbonate) which yields 5300 dKH. In recipe #2 you are doing essentially the same thing without drying (but making it 1/2 the strength by using half the weight and yielding half the dKH). So I'm guessing the weight of the soda ash resulting in recipe #1 is not 594 gm but something less, correct?


BRS provides "numbers" so I found these weights would yield the same dKH:

Soda Ash: 381 gm to 1 gal. makes twice the dKH as the bicarbonate (below) so 1/2 of 381 gm = 190.5 gm in 1 gallon

Bicarbonate: 302 gm to 1 gallon.

Is this correct? If so, then according to the BRS calculator, 71.4 ml of either solution should raise 100 gal by 1 dKH.


Does this mean that baking 302 gm of baking soda would yield 190.5 gm soda ash?

(Again, my reason for doing this is so I can mix the two solutions at any ratio, determined by the affect on pH being targeted, without altering the dKH.)

Thanks for helping.
Jim

 

[Randy Holmes-Farley Verified Community Expert]

Randy, I was thinking that the weight would be different after baking.

I'm getting confused between threads. I would not bake these unless the intent is to drive off CO2.

If you make my Recipe 1 at half strength (same water, half the solids), it can be combined with Recipe 2 in any amount and the alk potency remains the same as the recipe 2.

 

[Dr. Jim]

I'm getting confused between threads. I would not bake these unless the intent is to drive off CO2.

If you make my Recipe 1 at half strength (same water, half the solids), it can be combined with Recipe 2 in any amount and the alk potency remains the same as the recipe 2.

I know that bicarb has a temporary lowering affect on pH. I can't find where I read the amount of carbonate that needs to be added to make a mixture that has zero affect on pH (when the starting pH is around 8.2). Is the ratio about 1:14 by volume (carb:bicarb) when each yields the same dKH? Thanks.

 

[Randy Holmes-Farley Verified Community Expert]

The ratio depends on the pH that you want to keep fixed. More carbonate stabilizes a higher pH. It essentially matches the ratio of bicarbonate to carbonate present in the water at that pH. At normal tank pH it is mostly bicarbonate and a little carbonate, though I also see no special reason this ratio should be used.

 

[Dr. Jim]

The ratio depends on the pH that you want to keep fixed. More carbonate stabilizes a higher pH. It essentially matches the ratio of bicarbonate to carbonate present in the water at that pH. At normal tank pH it is mostly bicarbonate and a little carbonate, though I also see no special reason this ratio should be used.

My plan is to have 2 reservoirs, one with carbonate and one with bicarbonate. My GHL Controller will use "pH Control" to determine which is dosed. I will set it so if the pH< 8.2 then the carbonate will be dosed; if 8.2 or greater, then bicarbonate will be dosed. (The dosing schedule is on a timer and since the same amount will always be dosed, I need to have the two solutions provide equal yields of dKH which is why I asked about this earlier).
And, I want to mix a little carbonate in with the bicarbonate to avoid the initial pH drop when using just bicarbonate which is the reason I was asking what ratio to use for a solution at pH 8.2.

I have since found the answer from an old post from @JimWelsh ,,,,thank you Jim. He wrote:

"According to the CO2_Sys spreadsheet (https://www.nodc.noaa.gov/ocads/oceans/CO2SYS/co2rprt.html), seawater with a salinity of 35, temperature of 25C, an alkalinity of 8.0 dKH, and a pH (NBS scale) of 8.2 has a molar bicarbonate:carbonate ratio of around 8.2:1. Converting that into a dry weight ratio of the two compounds by multiplying by the MW of sodium bicarbonate (84) divided by the MW of sodium carbonate (106), we get 8.2 * 84 / 106 = 6.5. So a 6.5:1 ratio of grams of sodium bicarbonate to sodium carbonate should give a pH of around 8.2 when dissolved in seawater."

The only thing is this 6.5:1 ratio is based on grams of carbonate and bicarbonate but I need to figure it out based on solutions that produce equal dKH yields. I should be able to do that though! Or, do I just use the 8.2:1 for this calculation?

Thank you both for helping!
Jim

 

[JimWelsh]

Or, do I just use the 8.2:1 for this calculation?

Yes, but only *if* the molar concentration of the two solutions is the same. If the alkalinity of the two solutions is the same, then you would need an 8.2:2 ratio by volume.

 

[Randy Holmes-Farley Verified Community Expert]

My plan is to have 2 reservoirs, one with carbonate and one with bicarbonate. My GHL Controller will use "pH Control" to determine which is dosed. I will set it so if the pH< 8.2 then the carbonate will be dosed; if 8.2 or greater, then bicarbonate will be dosed. (The dosing schedule is on a timer and since the same amount will always be dosed, I need to have the two solutions provide equal yields of dKH which is why I asked about this earlier).
And, I want to mix a little carbonate in with the bicarbonate to avoid the initial pH drop when using just bicarbonate which is the reason I was asking what ratio to use for a solution at pH 8.2.

I have since found the answer from an old post from @JimWelsh ,,,,thank you Jim. He wrote:

"According to the CO2_Sys spreadsheet (https://www.nodc.noaa.gov/ocads/oceans/CO2SYS/co2rprt.html), seawater with a salinity of 35, temperature of 25C, an alkalinity of 8.0 dKH, and a pH (NBS scale) of 8.2 has a molar bicarbonate:carbonate ratio of around 8.2:1. Converting that into a dry weight ratio of the two compounds by multiplying by the MW of sodium bicarbonate (84) divided by the MW of sodium carbonate (106), we get 8.2 * 84 / 106 = 6.5. So a 6.5:1 ratio of grams of sodium bicarbonate to sodium carbonate should give a pH of around 8.2 when dissolved in seawater."

The only thing is this 6.5:1 ratio is based on grams of carbonate and bicarbonate but I need to figure it out based on solutions that produce equal dKH yields. I should be able to do that though! Or, do I just use the 8.2:1 for this calculation?

Thank you both for helping!
Jim

I have to say, this sounds way over the top to me.

The pH drop from dosing pure sodium bicarbonate all at once is only about 0.06 pH units for a 1.4 dKH boost. Since you presumably are not ever planning to add that much at once ,the "actual" drop on any controller addition is likely to be undetectable.

That said, and as Jim noted, if you are in seawater with a molar ratio of bicarbonate to carbonate of 8:1, and if you want to get there by combining the two equal-alkalinity solutions that I previously mentioned (the Recipe 1 carbonate solution diluted by half and the Recipe 2 bicarbonate solution as is), then you need to combine 1 part of the carbonate solution to 4 parts of the bicarbonate solution, because the carbonate solution (at equal alkalinity) has half as many carbonates as the bicarbonate solution has bicarbonates.

 

[Dr. Jim]

I have to say, this sounds way over the top to me.

The pH drop from dosing pure sodium bicarbonate all at once is only about 0.06 pH units for a 1.4 dKH boost. Since you presumably are not ever planning to add that much at once ,the "actual" drop on any controller addition is likely to be undetectable.

That said, and as Jim noted, if you are in seawater with a molar ratio of bicarbonate to carbonate of 8:1, and if you want to get there by combining the two equal-alkalinity solutions that I previously mentioned (the Recipe 1 carbonate solution diluted by half and the Recipe 2 bicarbonate solution as is), then you need to combine 1 part of the carbonate solution to 4 parts of the bicarbonate solution, because the carbonate solution (at equal alkalinity) has half as many carbonates as the bicarbonate solution has bicarbonates.

Thanks Randy. I didn't realize that the pH drop is so insignificant. So in a more practical situation where one might add 0.5 dKH per day, the pH drop would be only 0.02. (But since I now know how to mix the solutions to prevent any pH drop, I might as well go ahead with it!) Of course the more important part, for my purpose of "using pH to control carbonate vs bicarbonate dosing" is knowing how to dilute separate solutions to yield equal dKH. So, thank you again for your help with this.

For anyone interested in seeing how I programmed this with a GHL Controller, you can view it here. (I'm not familiar with APEX but I'm sure it would be easy to program):
Using pH to Control Dosing of Bicarbonate vs Carbonate | REEF2REEF Saltwater and Reef Aquarium Forum