The likelihood is that the damage done from the ammonia and nitrite being high for some time.
If you have a breeder net, you could put the fish in there for a while to protect it.
Regarding changing your water for ammonia: https/www.hamzasreef.com/Contents/Calculators/FreeAmmonia.php Use this website. It tells you when your free ammonia (that which is actually the dangerous chemical)... keep that below 0.05 ppm.
For nitrite: Once you reach this point, salt can be used to prevent nitrite poisoning rather than water changes. This will speed up the cycle as you won't be removing the food source of the bacteria.
If you have a breeder net, you could put the fish in there for a while to protect it.
Regarding changing your water for ammonia: https/www.hamzasreef.com/Contents/Calculators/FreeAmmonia.php Use this website. It tells you when your free ammonia (that which is actually the dangerous chemical)... keep that below 0.05 ppm.
For nitrite: Once you reach this point, salt can be used to prevent nitrite poisoning rather than water changes. This will speed up the cycle as you won't be removing the food source of the bacteria.