Oscars are very messy eaters and the nature of their diet will likely have an impact on the timing and frequency of tank cleaning.  For instance, Oscars tend to spit out parts of live fish while eating. So if feeding live fish, it is likely you will have to clean their tank more thoroughly and more often.

Water Changes: 25-50% water change weekly
Ph range: 6.5-7.2
Brackish: No
Water Movement: Weak - Oscars prefer slow moving water, they also require the high oxygen levels normally incurred by quicker moving water.
Water Region: All