I am currently dosing both. I know this is an old thread but for others that might come across this thread the way I did, ...Google, I thought I'd add my 2 centavos.
I have a little bit of everything in my 70gal tank. I just got an elegance coral and found out its from Indonesia... It's been in my tank so I want to treat the whole tank to make sure all the Indonesian elegance killer is dead. I'm on day 3 of using both melafix and pimafix at the same time. Everything gets angry when I add it, especially my clams (derasa and maxima), but an hour later everything looks fine. My crabs and delicate coral banded cleaner shrimp seem unaffected. Xenia keeps pulsing away even when the palys around it close up. I was a little scared when my rock/flower anemones basically turned inside out. their mouth distended in a big bubble. this could have been from the numbing effect these products have. in an hour they looked happy again. my condylactis shrunk initially but came back just fine. Shrooms did the same. Palys and zoas closed up but were fine in about half an hour. Fish all seem fine. No deaths, though some things were obviously irritated. I would imagine it's a little like Icy-Hot (but not as intense). It burns a little but once it soaks in, it's very relaxing.
***My system has good surface agitation and I am running an air pump just to be safe. I think the problem many people have with this stuff, and some other treatments like algaecides, is oxygen depletion.***
I got my elegance coral a little over a week ago. On day three it started closing mid-day. Bad sign. No tissue recession, but I figured I better do something before its too late. After 3 days of dosing, things seem to be a little less irritated when I add it. The elegance is fully expanding now so I think it is helping. Fingers crossed.