It depends on what type of corals you keep. If you keep soft corals your calcium and alkalinity can be lower. Low end of calcium is 380 but that would be soft corals and is still lower than I would like to run. LPS and SPS can vary, but 420-450(some will run elevated levels-pros and cons). Alkalinity should run 7ish to 8ish IMO no matter what, but people run this higher too. My salt mix comes in at +/- 11 dkh and 420-450 calcium. IMO the benefit to higher levels in an SPS tank is if you have high consumption you are less likely to have drastic swings resulting in your calcium and alkalinity getting too low as you will probably dose once a day. Too high and you don’t have the room for error if you mess up, easier to overdose. A lot plays into it. Soft corals are very dependent on photosynthesis, but LPS and SPS need calcium and alkalinity to build their skeletal structures along with photosynthesis.