Sick Severum

[Bruce1975]

So I’ve had a golden severum for about 3 years now and over the past couple months he’s been losing scales, but the other fish has been fine in the tank. I’ve treated him with various medications hoping they would help but none have.
Now, the past few days he won’t eat and is breathing heavy, his color has even gotten slightly paler. He acts hungry but won’t try to eat. I’ve been doing water changes and did another last night as the ph and alkalinity was high, everything else was normal.
Does anyone have any idea what may be wrong with him and how to treat it? I bought some api ph up last night and added it to the tank and am going to test the water again later today.
I’ve also added an airstone in the tank as well to increase the oxygen. It’s a 125 gallon tank with him and a tiger Oscar. I have three filtration systems on the tank and a heater as well. He’s also been pooping only clear long strings…

 

[GaryE]

Scales don't fall off - they get removed. It may be time to ask the tiger oscar what happened. He or she knows...

 

[Innesfan]

Did you mean to say 'ph down' since your ph is already high? That said, I wouldn't suggest adding ph-adjustors. Between that and meds, you've been throwing a lot of stuff at your fish. I'd do frequent water changes instead which is also the best treatment for wounds. As @GaryE stated, missing scales are likely due to an aggressor. The only other possibilty is trauma such as the fish getting stuck somewhere and thrashing to free itself. Since you did not mention that I think @GaryE 's dx is correct.