reading tank chemistry from corals

[eric.battani]

I would like to get as much input on this topic as I can, to not only help myself out but other reef keepers as well.
I have always herd that your corals will tell you, a little before hand, when your tank chemistry starts to get off balance. Well I have personally owned a reef for 3 years and have yet to learn "how to read a coral". Now we all know (or at least I do lol) that when your chemistry is "off" your corals will not fully open, look there best or worse start to lose there tissue if the water is way out of balance. But I would like to know how corals behave when your ph is low/to high, alk is low/to high, cal is to low/to high. Also more to the point which corals do what, and how to recognize what it means before its way off balance.
The reason I wanted to start this thread is b/c I usually only test my chemistry on the weekend, and if I can learn how to read my corals, I will have an idea of what's going on before something bad happens and hopefully I can fix it. A lot can happen from Saturday to the next Saturday, and if I can catch something by reading my corals, lets say low alk on Tuesday, I can get started on it then by testing my alk to confirm what my reef is telling me and get started on fixing to problem. Thanks to all. Also pictures would be awesome if possible.

 

[backpack]

If my corals don't look fully opened when I look at them I test. If growth has tapered off I test. If I have a lot more skim mate than usual I test. If colors aren't great or algae is starting I do a wc.