Water problems?

I had posted about my big oranda and how he had been either sitting on the
bottom, or hovering up at the top of the tank. I took him out and put him
in a 6 gallon tank for 5 days, changing the water every day, all water
treated with CopperSafe. He was just fine, and got put back in the tank.
After a week of him being active and back to normal, he's started doing it
again. Now one of my others is acting a bit "tired" as well.

I'm starting to think that maybe I need to do a total water change? I did
over 50% last week and will again today.

4 full sized fish in a 40 gallon tank (two babies in a fry netting at the
top of the tank, only about 1/2 in long), Emperor filter, sand substrate, 6
plastic and ceramic based 'plants'.

Any other suggestions, or should I just plan for a total cleanout next
weekend?

Tahnk,

Devin