Two of my fish have open sores on their upper lips. I am treating them with Melafix. But there is a problem...
What filter do I use after I take the activated carbon filter out

I have used the Melafix for 4 days without a filter and the water is trying a brown color. My fish are pacus and I know they dirty the water fast. The sores are very large and do not look like they are healing. How long will I need to use Melafix to heal them.
Also I am using a filter system called ( Whisper 30-60). I have two on my 60 gal tank. Could someone tell me a better filter system that might clean the water better

One more thing.....what is the measurements for a 60 gal tank....last week I emptyed the tank and only counted 37 gal of water I put back in. The tank was sold to me as a 60 gal.
Sorry...I/m not very bright about fish tanks and fish.