My experience with the red sea ALK test is it reads low, med and high. It is not very accurate. It may be a consideration to re test your alk with a better test kit such of Salifert just to compare. Ditto for your CA level, just to be on the safe side, test it with another test kit just to verify it's accuracy.
Infrequently are Equal parts of carbonates and calcium needed to be added to aquariums, They should be tested for and supplemented accordingly. If you have been adding equal parts and were only testing calcium, easily your alk could end up excessively high. (or vise versa) But in the case of a excessively high ALK and the continued adding of carbonates and calcium, your calcium easily can precipitate out of the solution. Normally, but not always, there are physical indicators of this.
Your welcome to bring in a sample and we can double test your water to see if we can find any differences.