When you say your going to add a new filter, what do you mean?  

I'm asking because your biological filter in the tank has probably already taken a hit from the meds.  

Don't replace the filtering material, just rinse it really, really well.  

Go ahead and change out the charcoal if you want to stay on top of water clarity, but wait at least 7 to 10 days before adding meds, or the carbon will just remove the meds right back out of your tank.  Especially with Maracyn, you'll just be wasting your money.

I'd try to do some partial, 20% water changes daily, and NOT vacuum the gravel for about 5 days and see where that gets you before starting another medication cycle.

My last two gups seem to be doing better now that I've actually stopped the Maracyn treatment and their water has cleared a bit.

One still seems to have some reddening by his gills, and they still don't seem to be moving quite right yet, but he pigged down his breakfast, so at least he's eating.

Think I'm gonna get some frozed brine shrimp today for the buggers.  Hey if I was 100 I'd want to eat like a king for my last suppers. :o)

gg
:o)