[greenoctopus]

I've been trying to work out how much CaO and/or CaCO3 is needed to bring sea water from pH 8.1 to 8.3, and then again at pH 7.9 to 8.3.  I've gone through the acid-base reactions and tried to work it out, but am quite confused as it is not as simple as I expected it was. 
If six major ions make up >99% of the total dissolved in seawater [sodium ion (Na+), chloride (Cl-), sulfate (SO42-), magnesium ion (Mg2+), calcium ion (Ca2+), and potassium ion (K+)], I wasn't sure how this would effect working out the equation, and how different would the result come out than if simplifying it by using regular H2O set at pH 7.9 and 8.1 to bring both up to pH 8.3?  How would the 3.5% salinity effect the amount of CaO or CaCO3 you needed to add? 

Any help with setting up and working out the equation is appreciated.

[Arkcon]

You should probably determine this experimentally with a small sample, then scale up and recheck for a larger volume.  You can't really calculate, because you don't really know the acid you're working with.  You have to account for the slight effect of other ions and salinity.  And you've selected two compounds that are sparingly soluble.

[Borek]

Seawater is not that simple. Experimental approach would be best.