That is easy.
Ammomia 0
Nitrite 0
Nitrate -try and maintain levels below 40 ppm at all times, obviously the lower the better.
PH - ideally no higher than 7.0 and no lower than 6.0, in other words you are better off with a more acidic than alkaline water
Edit
The last part of my post may be a little confusing. I'm not suggesting that a pH above 7.0 is harmful, however, many South American fish prefer an acidic water over an alkaline water. Whereas oscars can live perfectly okay in pH up to 8.0, water conditions are that much more critical with a high pH, so if possible, always keep your pH below, but don't do it with chemicals, use some wood if you want to bring your pH down naturally.
