Oh, heres some stuff you may or may not know about water chemistry, (im a B.Sc. Chemistry student btw so I know what I'm talking about). Your salitiy can be prefect, but like someone else said it doesnt mean anything alse is good, your water could be filled with just one salt like KCl, or NaCl or CaCo3 or MgCo3... or any other salt for that matter, it says nothing about the balances. Since water can only dissolve so much salt at that temperature, so if you test your water and find it to be 300ppm Calcium, it means something else is filling the gap, if your calcium is 600ppm it means something else is missing, the problem is, trying to get that ballance back can be almost impossible without alot of water changes, as each salt has different solubilities. So say you add Magnesium to bring down your Calcium, that doesnt mean it will work for sure, it mite work by percipitating out some of the calcium (turning it back into a non-disolved solid), or you may just increase your salinity, or it may not disolve at all.
BUT like i said, if one thing is high, it means another is lacking (dont dose for traces... they are called trace for a reason, you only need TEENY amounts and more can be toxic), I recomend water changes, and some dosing, also you need to keep an eye on the parms untill they stabalize, and when you have large corals (stonies in particular) you need to dose on a regular basis to maintain these balanaces so you dont have to fix them again. If your really good, you can do the math, and dose litterally the exact amount required to replace what is being lost in your tank... but most people dont know how to do that LOL.
