Water Treatment Calculator

[kane]

Hey guys,
So i usualy use grahams water treatment calculator. I had a bit of time on my hands so i've been trying to understand how it works.

Ok so if we take a water sample with:
Ca: 60
Mg: 24.5
Na: 14.5

CO3: 109.5 (from alkalinity of 182.5)
SO4: 45
Cl: 32

(i know these numbers dont work out exactly, but its what I have from my water report)

After addition of CRS to reduce the alkalinity (carbonates to ~15mg/L) the sulphate and chloride ions look like this:

Code: Select all

SO4: 121.3    Cl: 87.8

(So far so good!)

Now starting with a general purpose target, then changing to automatic and adjusting the Mg to 24.5 rather than 10 and setting a sulphate to chloride ratio of 2:1 gives a target of:

Code: Select all

Ca: 100.00    Mg: 24.50    Na: 20.00    CO3: 15.00    SO4: 211.20    Cl: 105.60

This gives required additions of:

Code: Select all

Ca: 40.00    Mg: 0.00    Na: 5.50    CO3: 0.00    SO4: 89.91    Cl: 17.82

I decided to calculate the amount of Gypsum to add to give the required Sulphate value to start with:

To get 89.91 mg/L of sulphate I calculated 161.9mg/L of Gypsum is required (the water treatment calculator gives 162.4 - so close enough given rounding etc)
An addition of 161.9mg/L will increase the amount of calcium by 37.5mg/L

I did a similar calculation for NaCl to give the required amount of Sodium (13.99mg/L NaCl required - again agreeing with the calculator - 13.98mg/L)

Now here is where the problem comes.
It seems in Grahams calculator he now takes the amount of calcium remaining (in this case 2.54mg/L) and calculates the calcium chloride addition from this (i think!) I get a result of 9.32 compared to 8.03 from his calculator.
But .... this now gives too few chloride ions.

However if you calculate the amount of CaCl2 based on chloride additions, you get an excess of about 8g/ml of Calcium (however the sulphate to chloride ratio remains at what it should be).

Now my question is would it be better to have an excess of calcium and the sulphate to chloride ratios match, or have the exact amount of calcium but with differing sulphate to chloride ratios?
(I know in the notes he suggests the ratio is quite subjective)

Or should it all exactly balance but doesnt because of the unequal initial ion balance?

Cheers,
Kane