My oscar got a strange mark on his head. he got it like 2 days ago out of nowhere. water parameters are perfect and he is acting normal and eating like a pig. he eats, crickets once a week and high quality cichlid pellets.
ibb.co/kDxcVa

If that mark just suddenly appeared, then its an injury. Maybe he jumped, rammed into something. It does look like erosion over time, like hole in the head. That however takes a long time to develop. Either way, its clean water that will heal. You may want to add a salt solution to protect from infection. 3 tblsp per 10 g. Bring to full dose over a 48hr period. If I may ask, how do you determine water parameters are perfect? Fish looks to have had problems before. Deformed jaw, slight cratering around that wound. Evidence of quite less than perfect water and/or general living conditions

Suprd71 wrote: If that mark just suddenly appeared, then its an injury. Maybe he jumped, rammed into something. It does look like erosion over time, like hole in the head. That however takes a long time to develop. Either way, its clean water that will heal. You may want to add a salt solution to protect from infection. 3 tblsp per 10 g. Bring to full dose over a 48hr period. If I may ask, how do you determine water parameters are perfect? Fish looks to have had problems before. Deformed jaw, slight cratering around that wound. Evidence of quite less than perfect water and/or general living conditions

this fish is a rescue. he was living in really bad conditions. he is now living in a 90 gallon tank, he gets 35% weekly water changes. he lives with a common pleco, raphael stripped catfish and i red tail shark and i know that is a bad idea but they were together when i got them. the oscar was huge already and he doesn't bother the shark. i know my water parameters are perfect since i use a water testing kit and the tank is cycled.
His jaw was already deformed when i got it from a friend that had him leaving in a small tank with water that looked like mud and the fish were dying of ammonia poisoning.
fish does not have trouble eating. he eats like a pig and his color is vibrant.

looks like a infected heater burn to me do you have a exposed heater? as Suprd71 said clean water and mabe a little salt should heal it just keep an eye on it.

if you don't mind me asking what do you use to test strips or liquid if you use liquid do you make sure to shake the nitrate test a lot

face mcshooty wrote: looks like a infected heater burn to me do you have a exposed heater? as Suprd71 said clean water and mabe a little salt should heal it just keep an eye on it.

if you don't mind me asking what do you use to test strips or liquid if you use liquid do you make sure to shake the nitrate test a lot

heater has a cover and i use liquid test kit.