A tip for some of the people who are newer to the hobby.

Over the last week or two I've talked to a couple of people who where having trouble getting corals to do well in their tanks.   I both cases it sounds like a case of the basic parameters being out of whack.
If you are running a fish only tank or fish only w/live rock (FOWLR), then the main things you only really need to worry about the basics:
Salinity: ~1.026
Temp: 76-82° F
PH: 8.0 - 8.4
Ammonia - 0!
Nitrite - 0!
Nitrate - As close to 0 as possible.
Phosphate - As close to 0 as possible.
When you add coral to the mix, things get a bit more complex, but if you keep the "Big 3" in check, you will most likely have success:
Calcium: ~420ppm
Alkalinity: ~9 dKH
Magnesium: >1350ppm
There is a fair range of "safe" values for Calcium and Alkalinity, but the key is that they must be "In Balance" in order for your corals to be able to make optimal use of them.    Magnesium needs to be kept above 1350 or it will be more difficult to keep CA and ALK in balance.
There are many resources on the internet that explain this in great detail (too much for me), but there is one in particular that I have found to be very useful:  The Reef Chemistry Calculator
The calculator will tell you exactly what you need to do to get your parameters in balance and it will also you exactly how much of your product of choice to add.
There are many other parameters that you can test for and there are many additives you can buy to supplement all kinds of stuff.  However, in my opinion there is no substitution for regular water changes with a quality reef salt.   If you keep up with your water changes you should be able to focus your efforts on the basics and the "big 3".
I hope that helps someone.
-JB