Heres a goofy way of looking at it.
The salinty of your tank is a total of all the elements that make it up. So if you run your tank at 35ppt or 1.026 you are going to have 35,000 parts.
So as a different way of looking at lets do this. Lets pretent that all the different elements (calcium, alk, mag and so on ) are marbles, each element a different colored marble. So if you ran your tank at 35ppt allthese 35000 marbles would fit into the bucket (bucket being the salinty level) not one more or one less then that level. Now at the 35ppt bucket you are going to have: 415 calcium marbles, 1290 ma marbles and so on in your bucket (alk at 8 dkh). Sooo ow what happens if you have a smaller bucket?? say your bucket will hold only 30ppt or 30000parts?? well its a smaller bucket so it will hold less marbles, if you are going to keep all the marbles in perfect balance then all the marbles should be reduced at the same percentage as the bucket was reduced. So in reducing the bucket size from 35000 to 30000 you have reduced the elements down 14%, Soo simple reduce the levels of the different elements by the same percentage and you are in balance but at a lower salinity?? So reducing calcium from 415 ppt at 35ppt to 30ppt (1.023) would mean 415 - 14%. Just do this with all the elements and you will be balanced.
Another way to use the marble analagy is as follows. If you have this bucket (salinity) that is equal to 30ppt or 1.023 the bucket is full, if you raise one of the elements beyond its balanced ammount either two things are going to happen. One is that you are going to need a bigger bucket to hold these extra elements (as in your salinty is going to go up) or some other color/kind of marble is going to fall out of the bucket (be percipated out of solution). So this would apply for say someone that runs a salinty at 1.023 and should have a calcium level of 356, now some folks run this salinty level but have a calcium level of 450. So what they are trying to do is to add almost a 100 parts to a bucket (salinity level) that cant take anymore marbles, so what ends up happening is that they push a 100 marbles (parts) out of the bucket. In most cases alk marbles.
anyway hope that helped and didnt make it more confusing.
mike