Baking Soda Dosing Calculations

sbash · Aug 2, 2017

Hi Folks,

I have having troubles with the online calculators for dosing baking soda.

For context, I have a few months left of travelling for a few weeks at a time and my tank (mixed reef, 220g) has reached the critical mass where the reef salts do not supply adequate nutrients; thus I needed to start dosing several months ago... Anyway, I can get away with irregular dosing of Magnesium and Calcium according to my tests; but the Alk drops way too much over a two week period. Which every two or three weeks, I bring it back up to 8-9dKH before I leave again. So, I ordered a proper doser; makes sense, right? However, it will not be delivered for another few weeks, so I rigged up a crude dosing system an aqualift aw-20 and a raspberry pi to use until then...

Now, before I head out of town again (lol, tomorrow), I need to get the dosing correct... Thus, I have a couple questions:

First, from July 16 to August 1st, the Alk dropped from 8.3 to 5.8; does this rate seem normal for a 220 gallon a moderate amount of SPS and LPS?

Next, the online calculators say this should take about five tablespoons, yet it only took me (just under) three. I did confirm it is sodium bicarbonate. Should I stick with my math to mix my dosing solution, or trust the calculators?

My Calcium is 450 and Magnesium is (a little low) at 1170. Hopefully I can rig up a second Pi-based doser for Mg today to help bring it up another 200 over the next couple weeks... Worse case, I will just dose a small amount, which will hopefully bring it up another 50 or so overnight...

I appreciate your thoughts, questions or concerns; Thanks!

Randy Holmes-Farley · Aug 2, 2017

Hard to judge daily demand from this data because it depends VERY strongly on the actual alk (lower demand at lower alkalinity), and will almost stop at 5.8 dKH. It doesn't seem unreasonable.

Without a doubt this calculator below is correct for mass based measurements, but you may be mis-estimating the actual water volume, or have some test inaccuracy, or if you are measuring based on dry solid volume, the material you are using may be more or less fluffy than was assumed for the calculator.

http://reef.diesyst.com/chemcalc/chem_calc3.html

sbash · Aug 2, 2017

Randy Holmes-Farley said:
Hard to judge daily demand from this data because it depends VERY strongly on the actual alk (lower demand at lower alkalinity), and will almost stop at 5.8 dKH. It doesn't seem unreasonable.

Without a doubt this calculator below is correct for mass based measurements, but you may be mis-estimating the actual water volume, or have some test inaccuracy, or if you are measuring based on dry solid volume, the material you are using may be more or less fluffy than was assumed for the calculator.

http://reef.diesyst.com/chemcalc/chem_calc3.html

Amazing, thanks, Randy!

I think you hit the nail on the head with the 'actual water volume'; I was using total system volume. I put a more appropriate estimate of my actual water volume and the result was much closer to the amount of baking soda I used.

Thanks again!