Water Parameters: Tolerates pH between 6-8, a General Hardness of anywhere from 5-19 dH, and a water temperature of about 72°F - 78°F. While this is a wide range, this doesn't mean your water can fluctuate between these extremes. Stability must be maintained or else it is extremely detrimental and sometimes fatal to the fish. Oscars are benthopelagic, meaning they swim and feed in open waters as well as on the bottom. They are typically found in shallower, slower moving waters, with sand or mud bottoms.
if the water is to cold will an Oscar not eat as much
You should also never forget to maintain optimum level of water temperature and pH. After the cycling process of 6 to 8 weeks, you need to introduce your Oscar fish into the water tank from plastic bag you bought from the fish store.
What temperature does your Oscar prefer? - Oscar Fish Advice Forum
Oscar Cichlid Care Tips
Tank Size: An Oscar aquarium should provide at least 30 gallons (114 litres) of space per Oscar in the tank.
Tank Setup: Oscars are notorious in destroying live or artificial plants in the aquarium. A driftwood, rock or similar hardy setup with lots of variations is best for an Oscar. Oscars love to dig a lot, so use a substrate accordingly.
Number of Fish: The Oscar Cichlid is not a schooling fish and hence can be kept alone in the tank. However if you wish to add more Oscars, ensure you meet the tank size requirements.
Water Filtration: Oscars are very messy. Perform weekly 10-15% water changes so that your Oscar always has clean water. Ensure you have a large filter which can filter the entire tank regularly. You can also have multiple smaller filters in the tank which could help preventing the risk of cycling your tank again after cleaning the filter media.
Water Temperature: The Oscar’s temperature should be 77 F (25 C), and ideally should remain between 74 and 81 F (23.5 and 27C). Keeping an Oscar too warm for long periods of time will result in Oxygen deprivation which could result in several complications in the Cichlid.
Water pH level: The Oscar Cichlid’s tank water needs to be slightly acidic at a pH ranging from 6.8 to 8.0.
Food: The Oscars are carnivores. Their preference is live food, small fish earthworms, brine shrimp for smaller Oscars. Resist the temptation to feed your fish every time you visit the tank. They are beggars and always act as if they are hungry.
Tank Mates & Other Fish: Oscar Cichlids is good with any other fish which is of equal in size. They tend to eat smaller fish thinking them to be food.
Seems like it's safe to say, 78-80 is the perfect temp