Just went through a 15% water change including a carbon/bio mass filter change. My Oscar now just "sits" up by the heater. He ate 2 meal worms prior to water change and the cloud fish swim around......any idea's?

Did you clean the filter media in tap water or tank water?

hello, did you totally replace your biomass or just rinced it in tankwater?
If you completely replaced it,your beneficial bacteria will be gone!
Then you'd have to recycle the filter.
We do not advice any carbon in your filter, only when you medicated the tank, to get remaint of the toxins out.

If your filter is cool, he may just be sulking....

if your fish is not gasping air or breathing heavy, no need to worry.
he/she mya just feeling the coldness of new water...and warm water near the
thermometer give him/her comfort.

Few questions, did you clean the filter in tank water

Was the new added water the same temperature as the tank water

If you answer yes to both of these then dont worry as he is probably just sulking

I want to thank all for responding......I've been rinsing the carbon in tank water after it has been siphoned out. I put the bio mass (old one) back in. This all worked cause now "oscar" is exhibiting his/her normal routines. Thanks again for your help..