OK this is going in another direction but here are my thoughts. The secret in keeping SPS is KH stability. At ca 400 the KH should be about 5.5. At ca 410 the KH should be 7. so if you aquarium uses 10ppm ca the KH should swing 1.5KH. Now if your ca is 450 the KH should be about 14 if your system uses 10ppm ca then at ca 440 the KH should be 11, a 3kh swing. It is far easier to keep a SPS tank stable at ca 410 kh 7 than it is at ca 450 and KH 14. Obviously the pH needs to be stable at 8.2-4