Save my tank!

[jason604]

Up until last week my tank been battling long hair algae and most my sps lost color and turned semi brown but my LPS and zoas were thriving. Till the first day of the semi crash I saw most of my sps frags totally dead overnight with its skin peeled off but doesn't look like RTN. Some of my largest colonies are having STN. None of my zoas of diff types are opened and LPS are opened a lol smaller than usual but still looks healthy. I did a large 40g water change for my 75g system and it seem to have help stopped the sps wipeout so far but colonies still STN. The first night that I notice my sps dying I did a water test and saw my KH was around 9. I always keep my KH around 7 and I normally always have a problem with it dropped but I don't now how it raised. I use a auto doser and the amt I dose is always the same. My cal and mag is the same as it's always been ca 330 an mag mid 1300s. I rly need help I am lost in what to from
Here and any tip will help. Or even if someone is nice enough to come over and see my system to see what I am doing wrong or can improve on.