It never fails to amaze me what these lunkheads at local fish stores will tell you. Gee, we sell magnesium and strontium products, they must be good for your tank...

Most real authorities, like leading authors/scientists with actual degrees and experience will tell you to not add any supplements other than calcium and carbonates. ESPECIALLY heavy metals like strontium and magnesium, if you can't test for them. Most salt mixes have way more of this stuff than exists in NSW. BTW, for buffer, you can safely and cheaply use baking soda. For kalkwasser mix, use pickling lime. You can walk out of HEB with several months supply of all the additives you need for about $2.

About the coralline, it would be helpful to know what's in your tank and what kind of light you have. 450ppm Ca and 4.0meq/l Alk are both quite high levels, higher than exist in NSW. If you've never added buffer or a calcium supplement, you must have a very low calcium load, or a lot of freshly added ASW. Probably your test kits might be reading high as well, as most commercial salt mixes like IO mix to less than those values. Don't worry, though, your tank is fine. If you're worried about ph, which i wouldn't be (unless you have a decent ph probe, you don't really know what it is anyway) you could mix up a teaspoon of pickling lime in some RO water (like a quart) and add it to your tank, a few slurps at a time over a several hour period.

Sorry for the rant. After a particularly odious experience with one of our lfs and aquarium manufacturers, I'm getting cranky.

Matt