[alexk3954]

Hi everyone,

I am trying to create some concentrated supplements for use in reef aquariums.  I am making supplements for Mg, Ca, and alkalinity (NaCO₃).  I don't know if I am mistaken in my calculations, but when I try to prepare the supplements on a large scale, I am unable to get my solids to dissolve, even though I am below the limit of solubility.

For example, I am trying to make a solution of sodium carbonate to supplement alkalinity.  Carbonate is utilized by corals to create a calcium carbonate skeleton.  Carbonate and bicarbonate levels are estimated by measuring total alkalinity, which is measured by adding acid to lower the pH to a certain level. The units used are molar equivalents (meq).  1 mmol of carbonate is therefore 2 meq because it can accept two protons.

I am trying to make a solution that is 3,000 meq/L.  Here is how I calculated how much sodium carbonate is required for 1 gallon of solution. 

(3.785 L/1)(3,000meq/L)(1 mmol NaCO₃/2meq)(105.9885 mg NaCO₃/1mmol NaCO₃)(1 g/ 1000mg) = 601.8 g NaCO₃

601.8 g / 3.785 L = 159 g/L

The solubility of NaCO₃ is 215 g/L

I am adding the NaCO₃ to a bucket and then adding enough water to fill to the 1 gallon mark.  After 2 days of stirring there is still a large amount of solid on the bottom.

I was under the impression that we were using reverse osmosis/ deionized water (RO/DI), but my boss is now telling me that he took the DI portion off of the water filter so our water is only RO.  I am going to have the DI reinstalled to see if that helps with solubility issues, but are my calculations correct? 

Could it be that whatever impurities that are left after the RO treatment are causing drastic decrease in solubility?

[billnotgatez]

NaHCO3
Sodium bicarbonate (Baking soda, nahcolite, sodium hydrogencarbonate)
Solubility in water
69 g/L (0 °C)
96 g/L (20 °C)
165 g/L (60 °C)
236 g/L (100 °C)


Na2CO3
Sodium carbonate (Soda ash, Washing soda, Soda crystals)
Solubility in water
71 g/L (0 °C)
215 g/L (20 °C)
455 g/L (100 °C)