[PCCMNL]

I am not a chemist or have any profession on chemistry but i do have a question and i hope you understand it here goes: 

-I have a solution of KMnO4(Potassium PerManganate), 
20Kg KMnO4 is mixed with 620L H2O which I believe yields = 3.22% concentration of KMnO4 and [with a of Ph = 8 or 10?i will
have to test this tomorrow.]

-KMnO4 is now constantly bubbled with CO2 gas which dilutes the concentration and after a while(days) some KMnO4 +H2O liquid dries up and Ph is now less than before therefore assuming that my concentration of KMnO4 is now less(?).


1.) How do I determine the spent concentration of KMnO4? [my only apparatus is a Ph meter, a sight glass to measure height of my solution in container, and my eyes to see the color of KMnO4]   


2.) How do I compute for make-up concentration ratio (KMnO4 Kg / H2O L) in order that my spent KMnO4 gets back to 3.22%
concentration? 

[Borek]

Bubbling CO₂ may dry out the solution INCREASING permanganate concentration - add enough water to get the level of the solution to the initial value and you are back to initial concentration. If anything reacts with permanganate, it is not CO₂. Quite possible that permanganate decomposes. No simple method of its concentration determination (that is, no simple method that can use only things you have at hand).

[PCCMNL]

Bubbling CO₂ may dry out the solution INCREASING permanganate concentration - add enough water to get the level of the solution to the initial value and you are back to initial concentration. If anything reacts with permanganate, it is not CO₂. Quite possible that permanganate decomposes. No simple method of its concentration determination (that is, no simple method that can use only things you have at hand).

as for bubbling co₂ isnt it that the permanganate gets spent since we are reacting it to other contaminants the co₂ injected on the KMnO₄ is not pure we are consistently removing the H₂S and Sulfur etc with KMnO₄? thus giving it a brown color and concentration is lower? 
is there any way of determining the concentration? are there any apparatus' or methods? thanks

[Borek]

Contaminants are not CO₂.

As for methods - spectroscopy or just a simple http://www.titrations.info/permanganate-titration comes to mind.