1- how big is your tank?
2nd why are you mixing these fish?
3rd how oiften are you getting on top of the waterconditions? are you testing your Nitrate/nitrite and ammonia?
I know you said you did a waterchange but how were the conditions before this?
My tank is a 55 gallon,i probaly had the tank for 2 months. The levels were high at first the guy called it "a growth cycle" so i added Bio-spiora. I perform weekly water changes with Kordons Amquel plus the guy said 2 uses this product and the only thing i worry bout is changing the water.I keep the Oscar because the guy that had him was using him as a feeder to 7 inch caribe 5 of them. please give input.