omykiss001
Active Member
I’ve got a question for Randy or any other chemistry savvy reefer. Mostly I’m looking to make sure my general chem skills and logic of calculation are correct and I’m not missing anything in my thinking.
I’m looking to have a more quantitative approach to dosing alkalinity in my tank. I’m using the BRS soda ash for alk dosing ATM. Rather than using volume to measure the soda ash I used a calibrated balance at work that is accurate to a 1/100 of a gram. I used their volume guidelines and measured out 2 cups of soda ash which had a mass of 400.18 g. I dissolve this in about 3L of RO/DI water then bring the final volume to 3.75 L (approx. 1 gallon).
What I want to do is use the concentration of my solution to calculate the starting and or maintenance dose for my reef tank. I asked BRS for the MSDS for their 2 part which they sent my way. According to this document their soda ash is: 100% Sodium Carbonate (mol weight 105.99 g/mol). I suspect it’s not this pure, but hopefully close
Other molecules to consider in my calculations.
Using the data from the MSDS and molecular weights provided above I can convert this amount of sodium carbonate (Na2CO3) back to mg/L of carbonate 60,420 mg/L [CO3] or 100,774 mg/L [CaCO3] equivalents in the BRS stock solution when dissolving 400.18g into total final volume of 3.75 L.
I use a Hanna checker for alk which reports out in ppm CaCO3 (yes, I know it is measuring total alk not just CO3).
In this example my Hanna checker reads 147 ppm (mg/L) and I’d like my alk to be around 160 ppm (~8.96 dKh). I need to raise the tank alk by 13 ppm CaCO3 equivalents and I have 150 gallons (567 L) water volume. Long term plan is to then get a daily usage and use this same thought process for daily automated dosing.
So 13 ppm CaCO3 in 567 L of water is 7,371 mg of CaCO3 that needs to be added to bring it to 160 ppm.
7,371 mg of CaCO3 is equal in moles of carbonate to 4,419 mg of CO3 or 7,806 mg of Na2CO3 (soda ash)
Using the stock solution concentration of 60,420 mg/L [CO3] or 100,774 g/L [CaCO3] I should in theory add 73.1 mL of the stock Na2CO3 (soda ash) solution to bring the ppm up to 160.
When I look at the BRS online calculators if I were to add dry soda ash I should add 7.8g or 7,800 mg which is dead on in line with conversion of 7,371mg CaCO3 to Na2CO3 from above. The BRS alkalinity calculator for 2 part solution is 77.8 mL which is close to my prediction and the difference I would attribute to the mass difference of my 2 cups vs. their 2 cups, theirs has slightly less material than my solution or they add a bit more RO/DI.
Anyone see any major errors in my thinking here. I can quickly convert Hanna reading to the mass needed for the Sodium Carbonate stock solution by just using the 100,744 mg/L CaCO3 equivalents the stock solution represents (easiest way by far).
using :
V1*C1=V2*C2 and solving for V2
we get (13 ppm [CaCO3]*567 L tank volume)/100,774 ppm [CaCO3] equivalents in stock solution = 0.0731 L (or 73.1 mL of stock solution) added to tank to bring alk up 13 ppm
While the online calculators are nice there is some assumption that your measurement of volume of a solid and theirs is in line, and for some reason they stop working if your internet goes down
. I prefer to use mass whenever possible as this does not change based on how much you pack or level the volume container. I am seeing about 6% measurement error based on what the BRS calculator and my calculations indicate for the solution route, but dead on for dry material. It’s not much, but I’m just trying to reduce the amount of fine tuning in my dosing schedule so removal of these errors I think will help, even if just a little. I'm sure the errors between their calculator and what the average guy measures out don't make that much of a overall difference and certainly won't overdose your tank if you follow their recommendations, but I’m kind of a geek at heart and like to do this stuff and one of the reasons I enjoy the reef tank so much being a mix of biology and chemistry in my living room
Thanks for the help validating my thoughts and yes I know I'm probably overthinking the problem/solution.
I’m looking to have a more quantitative approach to dosing alkalinity in my tank. I’m using the BRS soda ash for alk dosing ATM. Rather than using volume to measure the soda ash I used a calibrated balance at work that is accurate to a 1/100 of a gram. I used their volume guidelines and measured out 2 cups of soda ash which had a mass of 400.18 g. I dissolve this in about 3L of RO/DI water then bring the final volume to 3.75 L (approx. 1 gallon).
What I want to do is use the concentration of my solution to calculate the starting and or maintenance dose for my reef tank. I asked BRS for the MSDS for their 2 part which they sent my way. According to this document their soda ash is: 100% Sodium Carbonate (mol weight 105.99 g/mol). I suspect it’s not this pure, but hopefully close
Other molecules to consider in my calculations.
- Carbonate (mol weight 60.01 g/mol)
- Calcium Carbonate (mol weight 100.09 g/mol)
Using the data from the MSDS and molecular weights provided above I can convert this amount of sodium carbonate (Na2CO3) back to mg/L of carbonate 60,420 mg/L [CO3] or 100,774 mg/L [CaCO3] equivalents in the BRS stock solution when dissolving 400.18g into total final volume of 3.75 L.
I use a Hanna checker for alk which reports out in ppm CaCO3 (yes, I know it is measuring total alk not just CO3).
In this example my Hanna checker reads 147 ppm (mg/L) and I’d like my alk to be around 160 ppm (~8.96 dKh). I need to raise the tank alk by 13 ppm CaCO3 equivalents and I have 150 gallons (567 L) water volume. Long term plan is to then get a daily usage and use this same thought process for daily automated dosing.
So 13 ppm CaCO3 in 567 L of water is 7,371 mg of CaCO3 that needs to be added to bring it to 160 ppm.
7,371 mg of CaCO3 is equal in moles of carbonate to 4,419 mg of CO3 or 7,806 mg of Na2CO3 (soda ash)
Using the stock solution concentration of 60,420 mg/L [CO3] or 100,774 g/L [CaCO3] I should in theory add 73.1 mL of the stock Na2CO3 (soda ash) solution to bring the ppm up to 160.
When I look at the BRS online calculators if I were to add dry soda ash I should add 7.8g or 7,800 mg which is dead on in line with conversion of 7,371mg CaCO3 to Na2CO3 from above. The BRS alkalinity calculator for 2 part solution is 77.8 mL which is close to my prediction and the difference I would attribute to the mass difference of my 2 cups vs. their 2 cups, theirs has slightly less material than my solution or they add a bit more RO/DI.
Anyone see any major errors in my thinking here. I can quickly convert Hanna reading to the mass needed for the Sodium Carbonate stock solution by just using the 100,744 mg/L CaCO3 equivalents the stock solution represents (easiest way by far).
using :
V1*C1=V2*C2 and solving for V2
we get (13 ppm [CaCO3]*567 L tank volume)/100,774 ppm [CaCO3] equivalents in stock solution = 0.0731 L (or 73.1 mL of stock solution) added to tank to bring alk up 13 ppm
While the online calculators are nice there is some assumption that your measurement of volume of a solid and theirs is in line, and for some reason they stop working if your internet goes down
. I prefer to use mass whenever possible as this does not change based on how much you pack or level the volume container. I am seeing about 6% measurement error based on what the BRS calculator and my calculations indicate for the solution route, but dead on for dry material. It’s not much, but I’m just trying to reduce the amount of fine tuning in my dosing schedule so removal of these errors I think will help, even if just a little. I'm sure the errors between their calculator and what the average guy measures out don't make that much of a overall difference and certainly won't overdose your tank if you follow their recommendations, but I’m kind of a geek at heart and like to do this stuff and one of the reasons I enjoy the reef tank so much being a mix of biology and chemistry in my living room Thanks for the help validating my thoughts and yes I know I'm probably overthinking the problem/solution
.
