College Stats project: Relationship between 3 tank parameters

[MadSkillzMan]

hey guys, i've got a college stats class going here and one of our projects is a Correlation and Regression problem. Basically, the relationship between variables. We have to collect some recorded data samples, then plot it, then basically come up with an equation to try to predict some values from others.

We're on one now where we have to go out and collect data, and i figure hey why not a hobby i enjoy.

I was thinking something along the lines of relationship between Calcium/PH/GH/Temp/Alk or something of the sort..But it's beena while since i've fiddled witht hat stuff (so i'd probably be collecting data from you guys) so before i ask for data, i have to ask, what would you guys suggest i collect that would show a relationship between 3 variables? For example, in a FW tank, GH affects how easily it is to change the PH, but injecting CO2 will alter the PH, so based on the GH and PH we can calculate the CO2.

Thanks in advance guys.

[Randy Holmes-Farley]

pH and ORP are strongly correlated for a given aquarium. Almost perfectly correlated in known mathematical ways. That is true to a smaller extent of others as well (temperature and pH and ORP and O2, etc, driven by daily photosynthesis cycles, for example).

But as with almost all of these, they won't correlate much across different types of systems that have very different husbandry practices.

Time of day and pH and temperature aand ORP will also correlate, especially for a given tank.

[MadSkillzMan]

yea i was very much worried about that, iknew the different tanks would be an issue. So i have to find someone with a log of their tank.

Newb question, whats ORP:

[Boomer]

Mad

It is not GH but KH. GH = Ca++, Mg++, Sr++, Ba ++. And KH, Carbonate Alkalinity, is really Total Alkalinity. To calculate CO2 in seawater is another issue but it can be calculated. I have posted seawater equations on it here before and there is a elaborate program also to do this for seawater. For seawater you have to know the Salinity, pK₁ and pK₂ and the actual Carbonate Alk, which is TA - Borate Alk to include temp.

Here is the relationship of pH , Alk to CO2 for FW

CO2 Calculator and Tables for FW
http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

A simple equation for CO2 in FW is

CO2 ppm = 3 x KH x ^10(7-pH)

For seawater at 25 C and 35 ppt

CO2 = CA x pH / pK1 [1 +2 pK2/pH]

or

CO2 = {CA x 10 ^ -pH / [10^-pK1 (1 + 2 x10 ^-pK2/ 10^-pH ] } x 44 (molecular wt of CO2)


Example;

CA = 2.2 Carbonate Alk, the borate Alk has been subtracted, here .15 meq / l for a T-Alk of 2.35meq/ l

pH = 8.3 NBS

pK1 = 6.0 NBS

pK2 = 9.1


CO2 = { 2.2 x -log 8.15 / [ -log 6.0 (1 + 2 x -log 9.1/ -log 8.15 ] } x 44 (molecular wt of CO2)

CO2 = 0.56 mg / l CO2 dissolved in water

[MadSkillzMan]

Boomer,

Ok, i was just using CO2 as an example, and GH, yea i just knew that from FW tanks. I just figured i'd to PH/Ca cause i know that relates, i just needed a 3rd variable thats linked to atleast one of them.

wow thats alot of variables. Hah, i actually dont need to have any of the equations posted on here, what we'll simply do is place 3 variables in a table/plot/bellcurve, run it through this expensive software (Minitab) then create a Linreg/Quadreg y=ax+b equation. Then from the equation, we will have to take 2 of the 3 variables, and predict a 3rd one. Having the actual equations on here helps though just to compare how far off/accurate it is. Its more of a theoretical approach/class. What you've given me is actually far too accurate/complicated/right lol.

But i appreciate it! I actually have to run out and go work on it shortly.

Basically i guess bottom line what im asking is, what tank parameters should i ask for? I figure ill go bug the guys in my club forum for a log or someone over in just one of the general tank forums.