I don't know what magnesium does, let alone how to test or dose for it. I trust the salt I use to put in all that is needed, which is why I am such a religious believer in regular water changes. It just erases so many mistakes and imperfections with our systems.
As for coralline, you need to have a rock already in there to seed it. once it starts growing on the glass, I like to scrape it and it seems to float around in the tank and land other places. I know that high levels of cal and alk have something to do with it. I am no expert, just lucky I guess. Some people on this forum have learned through school, reading books, working is fish stores, etc. I learned what works through killing many things from stupidity. My goal now is to help someone else not be a stupid as I was.
Bobby. as for aquascaping, try looking a pictures of rock formations in the mountains or cool looking buildings and imagine in your mind's eye what that would look like as a reef. There, now you have my secret. I pass by a rock formation to work everyday that is really cool and that is what my current tank is based on. It works for me
-Doc