Tank crash

[Ram3500]

Well this has been a tough summer the bleaching started back in June with the heat wave and a chiller malfunction. It seamed like I had this under control with my chiller back online and the corals started to come around . I noticed my nitrate was a little high between 40-20 that was the end of July . I have been doing about 50 gal water change each week to try and get the nitrate under control . Last week I started doing about a 40 gal change ever day because the sps were looking a little pail . On Friday I did my weekly h20 test and my mag was at 800 ? WTF I have no idea how it dropped so low . I missed testing the water the week before because we when on a camping trip but how could it drop so low ?? Now I have lost four sps in the last three days ;( and what I have left is looking Very sad the only sps that still look good are my monti caps . My zoa garden thankful look good but I have four hammer colony's that are almost fully retracted . I have been trying to get the mag back up but It is a painful slow process I have it at 900 now . The good news is I finally found a way to kill all my Xenia. The salt mix I have been using is reef crystals . Not sure what to do any suggestions would be appreciated .