How much is too much?

I need new water. I tried 10% WC to try and gauge just what I needed by the difference in test results but have gotten little results so I know it's going to take a lot. My tank is so far outta whack on the cal, alk, mag side that idk how to fix it. Kh is so high, Cal is so low... someone else had been taking care of my tank for a while, and it's pretty jacked up. How much is too much? It's a 200 gal system that's been up and running for around a year. It is fully stocked and has several LPS corals and 2 SPS frags that have seen better days. My LPS are starting to go downhill now too. I read somewhere that the Kh will continue to go up with WC but down with time. Is this true?

For those who read this later, I changed water and the kh did go down. It took a long time but I finally got it right

 

What exactly are your readings? Sometimes depending on what kind and how many corals you have you may need to dose the tank to keep your levels were you want them. How often are you changing the water?The most important things to test are Cal,Mag, and Alk.Ideally if keeping sps you would want you ALK. To be at least 10. Calcium 450 and mag. at least 1350.Alk. at 11 Cal. at 500 and Mag. at 1500 would be even better.