If the amount of alkalinity in the effluent has dropped so has the amount of calcium. Its not possible any other way. The reason you may think that KH has dropped and CA has not is because calcium carbonate (ca reactor media) is mostly alkalinity.....the ratio I believe is 20:50ppm as in 20ppm of Calcium to 50ppm Alkalinity. Now since sea water has less alkalinity in it....say 130ppm (7.2dkh) than Calcium say 410ppm. Now if the alkalinity drops 50ppm and goes from 130ppm to 80ppm (or 7.2dkh to 4.5dkh) the calcium would only drop a meager 20ppm and go from 410ppm to 390ppm. Thus an illusion can be created that alkalinity has changed but calcium as not. Same reason why some people believe there tank needs more alkalinity than calcium....yes it does but it needs the same amount of balanced two part or balanced ca reactor effluent. Hope my ramblings make sense.
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