Quantitative effect on 2-part to pH

[Martin Kuhn]

We use 2 different salts to boost
- dosing NaHCO3 results in a slight drop of pH
- dosing Na2CO3 (soda ash) results in. Slight increase of pH
- dosing a combination of both is within between, if matched even neutral

Is there a way to estimate the effect that on ph .....
Knowing
- water volume of tank
- amount of 2 part salts dosed
(Only one type->which? Or maybe a mixture of both? How many % if both )

 

[GoVols]

Martin,
It's been a long time, and hope you've been doing well.

I'll tag along for the ride.

Freddie

 

[Conor Vaughn]

We use 2 different salts to boost
- dosing NaHCO3 results in a slight drop of pH
- dosing Na2CO3 (soda ash) results in. Slight increase of pH
- dosing a combination of both is within between, if matched even neutral

Is there a way to estimate the effect that on ph .....
Knowing
- water volume of tank
- amount of 2 part salts dosed
(Only one type->which? Or maybe a mixture of both? How many % if both )

I'll have to give a disclaimer and say that analytical chemistry wasn't my strongest subject in college, but I think the key to this is the Debye-Huckel equation (easily googled). You'll need to know the ions in your water, the salts that will become ions with rising pH (solubility change) and relative concentrations to one another. From there, you can calculate ionic strength (compounded) and activity (compounded) to determine the activity of hydrogen. The activity of H+ easily translated to pH by pH=-log activity H+. Link copied below to good description.

http://www.umich.edu/~chem241/lecture11final.pdf

This would be really complicated to figure out in the sense of knowing what all is in your water. I don't know if just knowing the major ions in solution would be sufficient. Maybe someone on here would have some short cuts.. rather than the really formal way I was taught.

 

[Randy Holmes-Farley Verified Community Expert]

We use 2 different salts to boost
- dosing NaHCO3 results in a slight drop of pH
- dosing Na2CO3 (soda ash) results in. Slight increase of pH
- dosing a combination of both is within between, if matched even neutral

Is there a way to estimate the effect that on ph .....
Knowing
- water volume of tank
- amount of 2 part salts dosed
(Only one type->which? Or maybe a mixture of both? How many % if both )

If you dose it such that the ratio of bicarbonate to carbonate matches that in the aquarium at the time of dosing (which depends on the actual pH), then it will have zero effect. For a normal reef tank that is mostly bicarbonate and a little carbonate.

I have measured the immediate effect of bicarbonate, carbonate, and hydroxide on pH, but calculating for complex mixtures added to a reef tank isn’t trivial.

As I showed in a reef question if the day, even adding pure water at pH 7 will raise the pH if seawater that starts at oH 8.2.

 

[Martin Kuhn]

My intention was not to be super accurate, but to add „some information“ to the users of different 2 part to my reef aquarium App.

Something like Apple is doing for their time prognosis for lengthy computer operations.

- this dosing slightly reduces your pH
- this dosing very slightly reduces your pH
- this dosing is nearly ph neutral
- this dosing very slightly increases your tanks pH
- this dosing slightly increases you tanks pH

However it would be good to have at least a certain indication
- How far a 100% Na2CO3 dose for a highly sps dominated tank would raise pH
- How far a 100% NaHCO3 dose for a highly sps dominated tank would lower pH

Any clue ?

 

[Conor Vaughn]

My intention was not to be super accurate, but to add „some information“ to the users of different 2 part to my reef aquarium App.

Something like Apple is doing for their time prognosis for lengthy computer operations.

- this dosing slightly reduces your pH
- this dosing very slightly reduces your pH
- this dosing is nearly ph neutral
- this dosing very slightly increases your tanks pH
- this dosing slightly increases you tanks pH

However it would be good to have at least a certain indication
- How far a 100% Na2CO3 dose for a highly sps dominated tank would raise pH
- How far a 100% NaHCO3 dose for a highly sps dominated tank would lower pH

Any clue ?

Sounds like that would be great info for people to have!

I think you could give someone a rule of thumb prognosis like that, but pH changes according to a sigmoid curve which means that as you add more Na2CO3 the pH wouldn't increase at a constant rate. It would reach a point when it would shoot up really fast. See graph-

The answer would depend on where on the graph the desired pH is (does somebody know this???). The sharper the angle of the line, the more necessary the super accurate calculations would be. on the graph above, you could give a rule of thumb dosing up to a little before the 1.0000 on the X-axis.

 

[Martin Kuhn]

Thanx Conor
unfortunately i don't understand what the diagram should tell me.

a very rough "estimation" of the effect on tanks pH could go in to simple steps and would look like this

1) decide if ph is "lowered", "raised" or even "buffered"
assuming that we have a possible combination of NaHCO3 (baking soda) and Na2CO3 (soda ash) in the recipee.
So if we define the %-age content of NaHCO3, we automatically get the content of Na2CO3 as it should be always 100 together.
(100%/0%, 90%/10%, 80%/20% and so on)
a) NaHCO3-% is between 90% - 100% -> decreases pH ("-1")
b) NaHCO3-% is between 10% - 90% -> more or less pH neutral ("0")
(i would expect as closer to 70% the more ph-neutral/buffered the recipe is)
c) NaHCO3-% is between 0% - 10% (more or less pure soda ash) -> Increases pH ("+1")

2.) Estimate "how strong" a lowering/raising effect would be
lets use the "daily demand of Alkalinity of the tank" as it is defining "how much" NaHCO3 and/or Na2CO3 is used
0..0,2 °dKH / per day: Estimated pH effect= result from 1) x 0
0,2..0,5 °dKH / per day: Estimated pH effect= result from 1) x 1,0
0,5..1,0 °dKH / per day: Estimated pH effect=result from 1) x 2,0
1,0..1,5 °dKH / per day: Estimated pH effect=result from 1) x 3,0
1,5..2,0 °dKH / per day: Estimated pH effect=result from 1) x 4,0

3. Come to an overvall estimation. If "Estimated pH effect" is between...
-3 .. -4 -> this dosing slightly reduces your pH
-1 .. -2 -> this dosing very slightly reduces your pH
0 -> this dosing is nearly ph neutral
+1 .. +2 -> this dosing very slightly increases your tanks pH
+3 .. +4 ->- this dosing slightly increases you tanks pH


What do you think?

kind rgds
Martin