Well for a start, you need to ensure the following:
1) Salinity 1.022 to 1.025
2) Ammonia = <0.25ppm (best is zero)
3) Nitrite = <0.05ppm (best is zero)
4) Nitrate = <10ppm (best is zero)
6) pH = 8.0 to 8.3
You can also check your KH (Carbonat Hardness) = 8ºkH to 10ºkH as a stable KH will ensure stable pH too.
Without a chiller, do take note of your highest temperature of the day and lower temperature of the day. The smaller the fluctuation within a day, the better. If you are just going FOWLR... 30ºC is still acceptable for most fishes although it is a little too close to the borderline.
All the best bro!!!