Yes, as poolboy just typed, it is perfectly normal to have to drain and refill the tub near the end of the very first month of ownership.
'Oz' is a non-chlorine shock or oxidizer. You will see people around here refer to that type of chem as 'shock,' 'mps,' 'oxidizer,' and other things along that line.
It doesn't take the place of chlorine, but it oxidizes the organic junk in the water, working in tandem with the ozone and the N2, giving the chlorine much less to do. As a result, you can get by with much less chlorine and still have a safe tub.
It sounds like you are doing things right - there are other products available which will do about the same. If you like LT - and it's as good a brand as any - you may want to try "Renew." That's pretty much the same as Oz but in a powdered form. You can add more or less that way, as needed.