Water changes are good Matt , but just be careful with the Alk levels.
I am saying this because this is something I am feeling disoriented. Let me explain. Around the start of 2015 I assembled my fuge / matrix system and systematically I was doing around 15% WC every weekend. During almost a year I NEVER measured alk in my Reef Crystal freshly prepared water. Since my change to AF and return to RC , with my Alk issues, I started to measured the Alk in the freshly done Reef Crystal water. Guess what..... I realized that is always around 9 dkh. Could it be this box I am using ? (I asked to myself) . But I started to search internet and found that my measurements were correct. RC salt has ~ that Alk levels when disolved, or more. I started to measured the tank before and after the WC and saw an increase in ~ 0.7 dkh in the DT after some hours of the WC. The WC is done in the fuge, and the full mix with old water is slow. The fuge gets the peak, but all the corals and a few SPS I have there are doing great.
Bottom line, before I was not paying attention to that detail and the tank was flourishing. But now that the corals are all stressed I try to be careful with the WC to avoid a new alk peak.
Sorry for the long post. I just wanted to share this that has been jumping in my head these last weeks.
Best
Daniel