There is much about your application that's hard to understand. You start with seawater being mentioned, then you don't mention it again. Your concentration of 2000 ppm is quite a high concentration, roughly 2x to 5x of other ions in sea water, so you're no longer talking about seawater, but instead a concentrated brine. Calcium lactate is a human dietary nutrient, its not particularly soluble, just reasonably well absorbed by the human GI tract, so I don't know why you picked that one over calcium chloride or calcium nitrate, unless you have to get your analytical reagents at the local drugstore. You haven't mentioned what buffers you've tried. And I don't understand how you call a solution of sodium carbonate and sodium hydroxide neutral.
Lucy, urm f0n4x:, you've got some 'splaning to do.