Don't let it get you down Draco,
I find S.W. to be somewhat like surfing (or snowboarding for us Canucks
). The tank is never really static. If your calcium has dropped in relation to increased C. algae growth this is due to the fact that the algae is taking the free calcium out of the water column and binding within its cells (a good thing). You may have to research some options like a calcium reactor, Kalkwasser or some other calcium suppliment. More frequent W/C's will help replace calcium as well.
I wouldn't discount the heat issue so quickly (though at this point it is a bit of a guessing game). Often a fish will encounter a stressor that weakens it and will linger for a while before dying. As if it has lost its will to live and is waiting for death to overtake it.
To continue the temp theme, for discussion sake:
If you have a smaller tank in a hot apartment you may want to look into some means of stabilizing the temp swings. It's not the high or low limits that will harm marine species so much but rather the swings back and forth. The first thing I would do is to start tracking your tank temps, particularily in the late afternoon/early evening, this is when your tank will have ramped up to its peak temp. Compare these to your morning temps. Since responding to the effect of the heat spell on my tank (opening all cabinet and hood doors, directing a fan at my sump, reducing my lighting duration) my temps have run 80 - 82F.
In the end we can only do our best. Test and correct. Good luck!
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herbalaire