Ozonizer!!!Help!!!!

[captaincrash4]

Hi everyone, I bought an ozonizer today (I got it of the internet) it all sounds good and when it turned up to day it looked good but the instructions are nt very good?It has an in and output on the back and I guess that I connect an air tube to the output and put it through an air stone (which I have done). I then switched it on and it makes a noice and lights up but it doesnt appear do do anything in the water??I know its probably right put if some one could tell me how to work one I would be grateful!! It has a dial on the from that starts at 0 , 15, 25 amd 50 and I dont understand what settings it should be at?

My tank is 15 gallon (no fish the tank is cycling) it has an filter and an air pump and stone!! The reason I got it is that During the year I plan on getting 100 -150 gallon tank and I thought it would be handy!!

If someone can please explain to me how to use it and what setting I should have it at so i can use it effectivly I would be greateful!!

Thanks!!