HI,
I am constantly trying to not kill my critters, two things that often get overlooked during that learning curve any of you taken basic chem may have heard of this term its a supersaturation.
Here's a wiki definition for you who missed the chem stuff.
Supersaturation - Wikipedia, the free encyclopedia
many of the elements in saltwater are at the thresh hold of a supersaturation and will only stay in solution if you keep it pretty well balanced ,the bad new is this coral, algae, inverts don't seem to utilize CA, MAG, KH at the same rate and the same system to system, so you are walking barefoot on broken glass trying not to upset the balance.
All newbies need to understand that change must be done very slow,things may take 24 hours to move up or down so adding more will over shoot, only move KH 1-2 points max. PH can be very unpredicatable so I tend to only watch KH and not worry to much about PH>
If your CA is High your MAG is low and your KH is pushing the limits you are at a supersaturation of CA at those levels and you will have a precip of Ca carbonate and it will fall like a rock using up your mag and the chain reaction has to run its course any drastic attempts to fix this will only continue the precip event.
Please read this article if your new it may prevent a disaster like I had, and save a few inverts lifes.
#1
Calcium and Alkalinity by Randy Holmes-Farley - Reefkeeping.com
#2
When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com
#3
A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com
IF I had read those three articles I would have saved alot of money using Kits to monitor KH,Phos,MG. Animals cost way more than test kits.I never had a problem with Ammonia,Nitrate, or other nasties cause of my DSB and skimmers,reforguims All though the water changes help if your not testing you may be only slightly adjusting or diluting your problem and it may contine to degrade with time. It may be perfect when you set up but that CA/ and mag go south pretty fast with algae, coraline and replacing with fresh synthetic may not keep up,
A newbie who learned thru that hardnock method..The pain of High mortality in you tanks its pretty bad when things go south and your favorite critter expire after having it a few weeks..
Doug
ps I now keep a saltwater diary and only attempt to adjust when things are below normal sea water CA 400, maG 1200, aND THAT KH, kALKWASSER is a good way to add Ca But it can spike the KH if your not real careful to avoid any of the precip in the solution ,it can spike the KH to over 20 ,most siphon off the clear liquid and add very slowly either by pumps or drip at night when the PH is at its lowest, but check your KH in teh AM if its High the next day and CA is stil below 400 I use only CA-CL powder no buffer go slow it can spike real fast pref mix in ro and add slowly to sump , that way you don't keep adding the the KH problem. KH starts the cascade and low mag will allow it to run wild. the buffer side of the equation , never is a problem in my systems its mostly CA & Mag,
I find weekly to every 2 weeks is more than enough testing and the CA, mag, KH seem to stay put try avoid tinkering just cause you can its not a good thing and any movement up or down seems to bother inverts..One thing that works for me if the anomone and the hermits are perky life is good if the ananome are shrinking most likely water quality is down, if I turn off my powerheads marineland filters and returns to adjust skimmer, and clean, for 20 mins they start to shrink, many they are touche. yikes
saltwater why is it so quick to change or crash 
, so you just put a heap in and wait ie: he 1/2 cycled and then put allsorts of things in the "chamber of death" (is what i call his tank) and he had a mass off blobbed out coral , dead fish and a empty wallet! (nothing that i could save)
but mine hasnt all died off but i shoulda learnt more about the chemistry in my tank befoer i added "1 of everything". 
