Stoney corals require many things to thrive. Once the basics are mastered, stability is most important. Keeping the parameters close to the natural sea water numbers will work every time as long as stability is considered. Chasing elevated parameters or sudden changes stress the corals greatly. Some believe keeping Calcium or Alkalinity at a elevated level can supply the animals with more of what they require. The problem is that a coral does not need more of these to grow and thrive. Trying to keep elevated levels creates a see saw effect and one or the other becomes out of balance quite often. Alkalinity in the approximate range of 7 dkh to 8 dkh if measured accurately is much easier to keep stable and sufficient for coral health. Calcium in the 380 ppm to 400 ppm is also sufficient. The balance of these two parameters is extremely important If one is allowed to rise greatly, the other will tend to drop from precipitation. Another key parameter to consider in Magnesium. Alkalinity and Calcium are difficult to keep stable if Mg is not kept at proper levels. A level of 1300 ppm to 1350 ppm is a sufficient density of this mineral. A better approach is to keep these closer to NSW and at a stable level. Using a balance additive to maintain these if any additions are necessary is the best practice. Some corals will not react extremely negative if this premise is not followed, but some sensitive stoney corals can loose tissue essentially over night Acropora species in general do not favor this instability. Soft corals will tolerate some abuse in this process and fare well when Acropora specimens will not. This can be a hard learned lesson when losses occur. It is best to follow mother nature in this regard and keep levels as close to NSW as possible. Keeping them very stable is also a very important factor. Chasing numbers without paying close attention to this may result in unnecessary loss and necrosis of your prize specimens.