2 part formula!

aaron23 · Jan 27, 2016

Good evening Randy!
It just struck me that using these 2 part calculator are great but what if the site goes down or something is wrong...

Can you briefly explain the formula behind the ca/alk dosing calculator? I'd like to try and understand it beyond just typing numbers into the calculator. Is it extremely difficult to understand?

Thank you!

Randy Holmes-Farley · Jan 28, 2016

I'm not sure which calculator you mean as there are different ones around, but here's the exact details of the recipe and the concentrations of the components that I recommend. BRS uses a slight variant, where they give you already baked baking soda (sodium carbonate), but the concentration is supposed to be the same:

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2006-02/rhf/index.php

and here's a good calculator if this is not the one you are using:

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

aaron23 · Jan 28, 2016

Ah Randy more specifically my question is, how does the alk calculator know how much alk is required to raise it from say 7.5 to 8dkh given the amount of aquarium water? What formula is used in the reef calculators for alkalinity

Randy Holmes-Farley · Jan 28, 2016

Oh, OK.

You have to start by knowing the concentration of the additive in some sort of units. For a liquid additive, that might just be dKH.

For example, my DIY Recipe #1 in the article is 5,300 dKH. So from that it is an ordinary dilution calculation.

If your tank is 100 gallons, and you want a 2 dKH rise, you need to dose 2 dKH * 100 gallons /5,300 dKH = 0.0377 gallons. Then convert that to other units such as mL.

For a dry supplement, you also need to know the concentration. Sodium carbonate, for example, has a molecular weight of 106 grams per mole. Being carbonate, it contains 2 equivalents of alkalinity per mole. So 100 grams contains:

Alk = 2 x 100 grams / 106 grams per mole = 1.89 equivalents of alkalinity.

If you dissolve that into a solution to make a total volume of 1 L, then that solution has a concentration of 1.89 equivalents per L, or 1,890 meq/L (the m is for milli). Since 1 meq/K = 2.8 dKH, then 1,890 meq/l = 5,283 dKH.

To use cups of dry powder instead of grams, you need to know how much a cup of dry supplement weighs, either by measuring it, or looking it up.