If you have to treat a fish, the coral skeletons and some sands will absorb copper and some other meds. This can complicate dosing and it will remain in the system forever.
Natural substrate may put your fish more at ease. You might consider silica sand as it doesn't suck up copper, like calcareous sands do. PVC elbows and t's make ideal shelters. They are cheap, non absorbing, and fish actually like them a lot. The only drawback is that it doesn't look good. You could use your corals most of the time, and keep the PVC on hand to replace them if you need to treat.
Hook up the Fluval to your main system for a few weeks to condition it, then move it to the q tank. Others will disagree but I don't think it's ready to support life yet. You need to boost the bacteria population in the filter quite a bit. I would add a single drop of ammonia to the q tank and wait for it to be broken down. Next add two drops of ammonia and wait. Keep increasing it each time. Soon you can add about eight drops and it will break down in hours instead of days. Test for nitrite and nitrate. If nitrite is zero and nitrate is high, it's ready for a complete water change and then a fish or two. You can maintain the q tank while there are no fish in it by adding ammonia regularly, and / or food. Just remember to do a big water change with water from the main tank because the nitrates will get pretty high. I hope this helps or gives you some ideas. It has worked for me. I only have two more fish that I want to go through the q system, then I'll probably break it down or use it for something else, like a nano.
