saturation calc

[Tammy3770]

before adjusting anything I need to know if it's broken,

After some maintenance on my calcium reactor, my alk jumped from 9.0 to 10.1 Dkh, which pushed my cal down from 420 to 410
My Mg is 1350. and Ph is 8.3
Reading through volume three Julian sprung,
It occurs to me that I need to know my alk/ca saturation condition. If it is above 1 I should be ok, Right?

So I need to know, a saturation calculator
and if the above Idea is correct.
Thanks

 

[Randy Holmes-Farley]

Saturation? It is about 4 in NSW, and you don't want it appreciably lower (and yours is not lower and is fine, all your values are spot on!).

This article may help:

Reef Aquarium Water Parameters
http://www.reefkeeping.com/issues/2004-05/rhf/index.htm

 

[Tammy3770]

I just wanted to know a value for my tank.
I want to record it for future reference
you know like: Ok my alk=, My ca=, and the Ph is =
so my aragonite saturation is ___
so its too high and I run the risk of calcium carbonate precipitation
or its way too low and no wonder why my corals wont grow.

Or if I were shooting for a saturation value, I could come up with scenarios to make that happen.

Isn't there a calculator for that?
and thanks for your response

 

[Randy Holmes-Farley]

Almost no one keeps track of the saturation index. Instead, they simply keep calcium, alkalinity, and pH in appropriate ranges (say, calcium of 380-450 ppm, alkalinity 2.5-5 meq/L = 7-11 dKH; pH 7.8 to 8.5, preferably 8.0 to 8.5).

But if you want to, you can download the calculator program that is here:


http://cdiac.esd.ornl.gov/oceans/co2rprt.html

FWIW, magnesium does not enter into such a calculation, despite playing an important role in preventing precipitation of calcium carbonate. That is because it does not change the saturation, but rather it keeps the calcium carbonate from precipitating even when the saturation index is high.

I discuss saturation in some detail in this article:

Calcium
http://www.advancedaquarist.com/issues/mar2002/chem.htm

 

[Tammy3770]

I dont think Its working for me or I don't understand it.
when I try to Download the CO2SYS.EXE Program
this is what I get,

This is CASE1.INP, a test program for CO2SYS. It works for case 1.
line1, 35., 3., 55., 20., 0, 5, 1000, 2400., 2200.
line2, 35., 0, 0, 20, 0, 5, 1000, 2400., 2300.
line3, 33., 2., 122., 15, 0, 5, 0, 2300., 2200.
line4, 35., 0, 0, 20, 0, 15, 0, 2300., 2100.
line5, 33., 3., 2., 25, 0, 10, 100, 2200., 2100.

I Know that omega={Ca2+}x{CO32-}/Ksp
but I'm not a chemist and cannot determine those values in my tank.
I was just hoping for a formula where omega can be represented as some combination of Ph, ALK, and CA. Things I can test and get a value for.
Like table 5.3 in Delbeek & Sprung volume 3. "the reef aquarium"
p242. The table credits you.

Does such a formula not exist?
Can you explain to me how I can get the values for this formula?
omega={Ca2+}x{CO32-}/Ksp

Its my understanding that 10 to 15 years ago "normal" people did not even change their tank water. Isn't this hobby about new ideas.
Thanks for your time.

 

[Randy Holmes-Farley]

Maybe it didn't work properly on your computer. There is not a simple equation to calculate it.

If you assume that nearly all of the alkalinity is due to carbonate/bicarbonate (true except in some salt mixes where borate is excessive), that the salinity is about 35 ppt, that the temperature is close to normal, and that the pH is below about 9, then you can estimate it as follows:

Omega = 3*(Calcium/420 ppm) x (alkalinity/2.4 meq/L) x pH correction factor

pH correction factor = 1 for pH = 8.2
multiply it by 2 for each 0.3 pH units above 8.2 (so 2 for pH 8.5)
multiply by 0.5 for each 0.3 pH units below 8.2 (so 0.5 for pH 7.9)

This gives the supersaturation index relative to aragonite formation.

 

[Tammy3770]

thank you,
would I have to convert ppm and meqL
in to some kind of agreeing measurement?

what does this * mean? times
thank you.

 

[Randy Holmes-Farley]

The * and x both mean times (sorry for the mixed usage ).

For alkalinity, 1 meq/L = 2.8 dKH = 50 ppm CaCO3 equivalents