Sorry, I was just trying to learn a little more about your situation Alexrd09 and thought I could share some of my experiences even though Kurt Nelson has you covered already.
for some reason they slowly died off only about 5 remain and i want to try to help them flourish
I've had similar 'luck' with zoas and some of the colony polyps, always just after I had brought them home and they have always (knock on wood) come back over time. However, I was pretty new to the world of corals then and I have since realized that taking the time to peek in on new (and old) corals can really pay off because they usually provide visual clues as to what they are experiencing.
While I am sure that some may disagree with me, but if you aren't already doing so, I feel as though it is beneficial to acclimate new corals just like you would acclimate a new fish. In fact, after having quite a few problems with corals I bought at one specific store I decided to mention it to one of their employees and found out that they maintain a much lower salinity in their tanks (I believe to combat ich, but that is another subject) that I do so some of my problems could have been caused by my failure to help them adjust more easily. If nothing else, perhaps it would be a good idea to ask your LFS about this sort of thing just in case it proves helpful in the future.
As Kurt Nelson pointed out, you should be able to keep a wide array of corals under your current light system but I wonder if your lights also have something to do with your zoa issues. Getting back to the potential differences between our tanks and an LFS' tanks, do you think it is possible that the store was keeping the zoas under much less intense lighting? If so, perhaps it is the shock of going from moderate to low lighting to your MH system and because of this, IMO it is also a good idea to help your new corals adjust to the new light conditions.
How often should i be doing a water change on this tank
Again, I also agree with Kurt Nelson in that a weekly 10% or biweekly 20% water change is a good rule of thumb but since I noticed in your other thread that you have a nitrate test kit, I suggest that you take a little extra time for frequent testing for nitrates over the course of the next several weeks. I'd also record each result because this will give you some clues as to how quickly nitrates accumulate over a given period of time. From there, you can simply set a "threshold" for nitrate levels and perform water changes based upon that. As Kurt Nelson alludes to, I think your relatively robust stocking will result in you having to perform bigger and/or more frequent water changes but this is why nitrates can become a valuable guage.
should i be adding any chemicals to the tank to help the corals
IMO, this is a hard question to ask because:
- It's never a great idea to start dosing all sorts of chemicals/products based upon a guess.
- The speed at which certain chemicals are used up and need to be replaced can vary dramatically from one tank to another and again, dosing blindly can be very risky.
- There is, most definitely, a lot of credence to the old adage, "too much of a good thing" and can apply to our hobby in any number of ways.
In short, I highly suggest picking up and using test kits to tell you when and/or if you need to supplement anything such as calcium. Otherwise, I think Purple Up is a pretty good product that will benefit a lot of your corals and even help promote coralline algae growth as well. However, I have enjoyed some positive results from using Kent's Essential Elements as well.