Sodium Carbonate vs bicarbonate

irvp13

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Hello,

I was in the market recently and I found out that some companies are seeling soda ash istead of baking soda.
what is the diference between using sodium carbonate nad sodium bicarboanate to dose Alk
My guess is that bicarbonate is more effective since it has more Carbonate?
What happens with the Na molecule after the reaction is made?

Thanks
 

Boomer

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Carbonate = CO3--
Bicarbonate = HCO3- ( the "Bi" means two, as in H + CO3)

pH = a measurement of H+ and the more H+ the lower the pH and less Alk in short. Molar value wise it takes twice as much as Bicrab as Carb to raise the Alk up 1 Eq unit. Volume wise it is 0.6 tsp of Bicrab vs 0.4 tsp of Carb to raise the Alk 1 meq / or 2.8 dKH in 10 gals. Weight wise is it is 3 grams vs 2 grams.

Bicarb, due to that H, has less impact on pH than Carb. Bicrab is mostly for raising the Alk and Carb is for raise the Alk and pH. Carb used only by itself should only be use if you low have pH and Alk. If it is to buffer up the Alk Bicrab is better. Many of the buffers you see being sold are mixtures Bicarb and Carb. If we look at NSW the amount of "carbonate " it is ~ 90 % Bicarb and 10 % Bicarb. So, if you were making your own it is about 10 parts to 1 part or to say 10 tsp Bicarb added to 1 tsp Carb. What ever the buffer is they should NOT be used 95 % of the time to raise the pH. Low pH 99 % of time is a CO2 issue. If you continue to try and bump up pH with a buffer the Alk will go through the roof. The pH does not care what the Alk is. If CO2 rises the pH will drop no mater what the Alk is. Meaning, you can have a higher pH with a lower Alk than one with a higher Alk and even the pH could be lower with that higher Alk. All just a function of CO2. It is really CO2 that controls the pH not the buffer. Same for the Ocean.

That Na+ more or less accumulates over time, as does the SO4 and Cl from other sup. Hence, WC. Only Kalk leaves nothing behind.
 

irvp13

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Thank you Bommer you always go above and beyond to support your answers!
I use bicarb only for my alk, but I've found that if my Alk is below 8 the PH will be around 7.8 in the mornings.
I strongly wanted to use Kalk for Ca and Alk but even at saturated solution the Kalk cannot keep the levels. Still it drops 3 points of dKh and 50ppm of Ca everyweek.
I guess I could try to increase my evaporation but I dont want to go into that.
 

Boomer

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50 ppm / week is a common number for sps calcium demand. You may want to think about a reactor not that you have to have one.

Alk is below 8 the PH will be around 7.8 in the mornings.

That pH drop is from "animals and Plants" giving off CO2 at night. The reason why it may not hold at a lower Alk is also a night thing of "animals and Plants"> "Leaching" out things more so, which can have a greater impact on the Alk and pH as they yield acids. A common limnological term for Alk is ANC, "Acid Neutralizing Capacity". These affect the pH and Alk. Although it is not often heard of in this hobby there is also Acidity, Acd, BNC, (Base Neutralizing Capacity) and yes there are even test kits for it :D. It is the opposite of Alk.
 
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