@Jake1508 I would be cautious mixing goldfish and oscars, goldfish prefer different temperatures to oscars, and if they are small enough to fit in the oscar's mouth, they may be eaten. As for how to take better care of the goldfish, I would suggest you either rehome the goldfish to someone with a suitable tank (preferably not the pet store, they'll just sell it back to someone who'll probably keep it in a bowl, not good), or buy a much larger tank (720+ litres), with a suitably powerful filter (it should completely turn over the tank's volume in water 6 times an hour, so a 720L tank would need a filter with a turnover rate of about 4320L/hour. The turnover rate of a filter should be printed on the box). Cycle the tank before you add anything, the resulting ammonia from not cycling will burn the fish's gills and they will become extremely stressed, if not die. Keep up regular water changes, 20% of the tank volume per week is a good starting point, but depending on your parameters (use a test kit to test for ammonia and nitrate weekly). Ammonia should always be at 0ppm, any detectable amount is bad. Nitrite should also be at 0ppm. Nitrate doesn't have to be exactly zero, but should always be less than 0.25ppm. Clean your filter media once a month (always rinse the media in tank water, never tap water. The chlorine/chloramine in tap water will kill the beneficial bacteria that live in the media that convert toxic ammonia into less toxic forms). Live plants are good, but not required. Feed only as much as your fish will eat in about 5 minutes, any food left after that time should be scooped out with a net/siphoned out. Use a siphon to vacuum the gravel during water changes to avoid poop buildup in the gravel. Before putting your hand in the tank for any reason, give your hands a good rinse under the tap (no soap), soap residue and other contaminants on you hands can seriously hurt your fish. You don't have to, but I would suggest naming the fish. It will help you get more attached to the fish and make you more motivated to take good care of them, it works for me. And be sure to enjoy your fish! Fishkeeping can be a very rewarding hobby if done right, so enjoy it!
@Jake1508 if there's no oscars, how is it an oscar tank? What is the capacity of the tank and other fish already in it? It could be a viable option for rehoming the goldfish.
